ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Male
  • Seismology
  • Industrial Chemistry
  • Inorganic Chemistry
  • 2020-2022  (27)
  • 2010-2014  (2,223)
  • 1950-1954  (2,980)
Collection
Language
Years
Year
  • 1
    Publication Date: 2021-03-29
    Description: Under certain conditions, ocean surface gravity waves (SGW) interact with the seafloor underneath to trigger relatively faint but measurable seismic waves known as ocean microseisms. Cyclonic storms (e.g. hurricanes, typhoons) wandering over the ocean are major (non-stationary) sources of the former, thus opening the possibility of tracking and studying cyclones by means of their corresponding microseims. For this purpose, we identified storm-related microseisms hidden in the ambient seismic wavefield via array processing. Polarization beamforming, a robust and well-known technique is implemented. The analyses hinge on surface waves (Love and Rayleigh) which, in contrast to P-waves, are stronger but only constrain direction of arrival (without source remoteness). We use a few land-based virtual seismic arrays surrounding the North Atlantic to investigate the signatures of major hurricanes in the microseismic band (0.05-0.16 Hz), in a joint attempt to continuously triangulate their tracks. Our findings show that storm microseisms are intermittently excited with modulated amplitude at localized oceanic regions, particularly over the shallow continental shelves and slopes, having maximum amplitudes virtually independent of storm category. In most cases no detection was possible over deep oceanic regions, nor at distant arrays. Additionally, the rear quadrants and trailing swells of the cyclone provide the optimum SGW spectrum for the generation of microseisms, often shifted more than 500 km off the "eye". As a result of the aforementioned and added to the strong attenuation of storm microseisms, the inversion of tracks or physical properties of storms using a few far-field arrays is discontinuous in most cases, being reliable only if benchmark atmospheric and/or oceanic data is available for comparison. Even if challenging due to the complexity of the coupled phenomena responsible for microseisms, the inversion of site properties, such as bathymetric parameters (e.g. depth, seabed geomorphology), near- bottom geology or SGW spectrum might be possible if storms are treated as natural sources in time-lapse ambient noise investigations. This will likely require near-field (land and underwater) observations using optimal arrays or dense, widespread sensor networks. Improved detection and understanding of ocean microseisms carries a great potential to contribute to mechanically coupled atmosphere-ocean-earth models.
    Description: Universität Hamburg
    Description: poster
    Keywords: 550 ; 621 ; 004 ; 534 ; Ambient seismic noise ; Seismology ; Oceanography ; Microseisms ; Cyclones ; Hurricanes ; Marine Geophysics ; Beamforming ; FID-GEO-DE-7
    Language: English
    Type: poster
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    facet.materialart.
    Unknown
    FISON | Lagos (Nigeria)
    In:  http://aquaticcommons.org/id/eprint/24627 | 19325 | 2018-05-22 06:26:49 | 24627 | Fisheries Society of Nigeria
    Publication Date: 2021-07-15
    Description: The 2661 specimens of the striped mullet, Mugil cephalus L. used for this study, were collected from high brackish lagoon in southwest Nigeria for 24 months. The size of the 2661 specimens of M. cephalus used for this study ranged from 1.7- 29.5cm standard length (total lenght 1.9 to 39.0cm). The sex ratio for M. cephalus was 1:0.53 and this showed a statistically significant (p〈0.05) dominance of the male over the females for the size range. The fecundity estimates varied from 635,568- 1,520,185 and was positively correlated to the fish and weight. Oocyte diameter averaged 409.64 ~c 40.67pm and this is indicative of an early stage of gonad maturation of the specimens in the lagoon before final spawning occurred. The GSI indicated that spawning activity occurred from December to May in the open ocean.
    Description: Includes: 28 references.
    Keywords: Ecology ; Fisheries ; Mugil cephalus ; ASE ; Nigeria ; Lagos Lagoon ; Mature ; Spawning ; Specimen ; Male ; Female ; brackishwater environment ; automation
    Repository Name: AquaDocs
    Type: conference_item , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 241-246
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25147 | 18721 | 2018-08-26 16:54:41 | 25147 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: This investigation carried out for the first time in Iran inorder to prodcution of monosex female and also sterilization in Rainbow trout. In this study, the eggs of general females were fertilized with the sperm of sex reversed male and so monosex female population was produced in second generation and sterilization carried out with oral administration of 17α methy 1 testosterone and immenrsion and oral administiration methods were used in embryonic stage and from commencing of acitve feeding of larvae, respectiverly. For sex reversal , 13 treatments were considered totally, that the most percentage of male (100%) was observedc in a treatment including of orally administration of 0.5 ppm hormone for 60 days after commencing active feeding (P〈0.001). In the other treamtnet, different percentages of sex ratio including male, female, intersex and sterility were observed. The offspring of genral eggs fertilization with the sperm of masculinized fish were 100% female, chisquare test was shown the treatment of orally administration of 30 ppm hormone for 120 days after commencing active feeding that had been considered for sterilization, was produced 90% sterile fish (P〈0.001) and was changed the sex ratio significancthy. Morphological changes of the gonads and sperm ducts in matured fish and also histological changes in the gonads of fish in the treamtints were considerable.
    Keywords: Biology ; Iran ; Monosex ; Female ; Male ; Sterilization ; Rainbow trout ; Eggs ; Fertilized ; Sperm ; Population ; Sex ; Fish ; Oncorhynchus mykiss ; Rainbow trout
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 58
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25193 | 18721 | 2018-09-03 17:21:38 | 25193 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: Aquaculture for human consuming species is being considered as the first substitution of catching aquatic species due to increase of human population and decrease of wild aquatic stocks. In this study, the hybrid sturgeon Bester (female beluga x male sterlet) was produced for the first time in Iran. Sperm of 1.35 kg male Acipenser ruthenus was used to fertilize the eggs of 125 kg female Huso huso in Shahid Marjani Sturgeon propagation center (Agh Ghala, Golestan province). The fries of bester and control treatment of beluga were transported to International Sturgeon Research Institute (Rasht) after about one month by reaching to 490 mg and 377 mg of weight respectively. All fishes fed by artificial concentrated food (48-50% protein and 15-17% fat) after a period of feeding with Artemia and Daphnia. Sorting was carried out according to increase of fish weight for both fishes. Results showed that the imported sterlet spawners were not at the high maturation stages and especially the males had not suitable sperm quality. It showed that up to 2 months of age , these was no significant difference between bester and beluga weight but from this age up to 2 months of age the weight of beluga was greater. Meanwhile from 2 months old up to the end of the study (21 months) the weight of bester sample was significantly greater than beluga. The comparison of FCR for the whole rearing period showed no difference between bester and beluga (2.4 and 2.3 respectively). In general, the increase and decrease pattern of GR and SGR were coincided to each other, but showed monthly differences. Growth rate (GR) and specific growth rate (SGR) of bester were greater than beluga from 4th and 3rd month of rearing period respectively.
    Keywords: Aquaculture ; Iran ; Golestan Province ; Aquaculture ; Beluga ; Sterlet ; Bester ; Growth Rate ; Aquatic ; Species ; Population ; Female ; Male ; Acipenser ruthenus ; Huso huso ; Sturgeon ; Artemia
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 55
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    facet.materialart.
    Unknown
    In:  http://aquaticcommons.org/id/eprint/26001 | 18721 | 2018-10-19 18:22:44 | 26001 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-24
    Description: Nonylphenol (NP) is an endocrine disrupting chemical which has been shown to be able tomodulate endocrine system of various organisms by different mechanisms. The objective of this study was to investigate the potential effects of 4-NP and 17-β - estradiol (E2) on the immune parameters (IgM levels and lysozyme activity) of the teleost Koi carp (Cyprinus carpio carpio) for a better understanding of the immunereproductive system interactions. The experimental fishes were injected with ascending doses (10, 50,100 μgg^-1 body weight) of 4- nonylphenol (4-NP) and (2 μgg^-1 body mass) of 17-β-estradiol (E2) or vehicle during 3 weeks. After 21 days, the fishes (180) were anesthetizedand their blood samples were collected from caudal vein, and then they were dissected and sexually separated by gonad characters. The measurement of immune parameters in plasma showed that 4-NP induced significant increase in the IgM levels and lysozyme activity at dose of 50 μgg^-1 while the levels of these parameters in the higher doses (100 μgg^-1) decreased compared with the control group (p〈0.05). In addition the treatment, with 2 μgg^-1 E2 significantly decreased both the IgM levels and lysozyme activity after 21 days of injection. These results indicated that 4-NP and E2 could lead to disturb the balance of immune system with potential consequences for immature koi carp.
    Keywords: Biology ; Pollution ; Iran ; 4-nonylphenol ; 17-β-estradiol ; Immune-reproductivesystem ; Immunoglobulin IgM ; Lysozyme ; Koi carp ; Cyprinus carpio carpio ; Disruption ; Growth performance ; Female ; Male
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 725-744
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25836 | 18721 | 2018-10-13 10:31:51 | 25836 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: The most important habitats of mudskippers are muddy areas in tidal zone of tropical mangrove forests. Mudskippers are related to Oxudercinae subfamily of Gobiid fishes. Three most distributed species of Hormozgan mudskippers were Periophthalmus waltoni, Boleophthalmus dussumieri and Scartelaos tenuis. These fishes can be considered as euryhaline and eurythermal aquatic species, because they can tolerate a wide range of salinity and temperature. A research was done since september 2008 to september 2009 in two important mangrove regions of Hormuzgan (Tyab and Khamir) to determine some ecological characteristics of inhabited mudskipper species. Results showed that nitrate levels are significantly different between tidal lines and seasons (P〈0.05). Maximum nitrite concentrations were recorded 53.2 and 92.5 µg/l in Khamir and Tyab respectively. The annual correlation matrix showed that a positive correlation between phosphate concentration and nitrite and silicate (P〈0.05). Silicate concentration was very high, because of too low density of diatoms and radiolarians. Some species of diatoms, dinoflagellates, cyanobacteria and larvae of crustacea and echinoderms were observed with different density and diversity. Sediment composition of the studied areas were categorized in three classes (clay, sand and clay - sand). Polychaetes formed dominant group of benthic fauna in Tyab and Khamir areas. High density of capitellid worms was possibly related to some environmntal stress caused by activity of fishing and cargo vessels. It was not observed significant difference between fishes length in two areas (P〈0.05); Mean lengths of P. waltoni, B. dussumieri and S. tenuis were calculated 9.85, 14.7 and 11.5 cm respectively. Spawning period of each three species in both areas were obtained from late winter to late spring based on gonadosomatic index values. Male to female sex ratio of P. waltoni, B. dussumieri and S. tenuis were calculated 1:0.45, 1:0.41and 1:0.74 respectively. Absolute fecundity of P. waltoni, B. dussumieri and S. tenuis were estimated 3558 ± 2202, 3952 ± 1030 and 6742 ± 1939 respectively. P. waltoni feeds mainly on fiddler crab, S. tenuis uses crustaceans and gastropods and B. dussumieri has a vegetarian diet.
    Keywords: Ecology ; Iran ; Persian Gulf ; Hormozgan Province ; Mudskippers ; Ecology ; Periophthalmus waltoni ; Boleophthalmus dussumieri ; Scartelaos tenuis ; Female ; Male ; Benthic fauna
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 97
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25845 | 18721 | 2018-10-13 08:35:24 | 25845 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: Biological characteristics of Liza klunzingeri were studied in two coastal areas, Sajaphi and Bahrekan, of eastern Khuzestan during March to February 2007. Among total 1880 measured fish specimens, 947 specimens were analyzed. The mean value of Gonado-somatic Index (GSI) for the male and female fish were calculated as 0.96± 1.39 and 3.25 ± 3.26 respectively. The GSI value was highest in November and lowest in July. The mean value of condition factor (K) was 1.25± 0.14 in male and 1.21± 0.15 for female. The highest K value were observed in June and the lowest value in February. The lenght at first maturity regardless of sexuality, was found to be 14.5 cm and the time of spawning based on reproduction pattern were determined in Nov- Dec. The length-weight relationship were calculated as Y=0.024L^2.76 (n=226R2=0.72) for males, Y=0.011L^3.00 (n=444R2= 0.78) for females and Y=0.0208L^2.82 (n=670R2 =0.82) for total fishes and also it’s found significant in level length weight relationship in (P〈0.05). According to biological characteristics and referring to American fisheries society (AFS) indices and Fuzzy logic expert system, Lize klunzingeri is classified as low vulnerable species.
    Keywords: Biology ; Iran ; Khuzestan province ; Sajaphi ; Bahrekan ; Lize klunzinger ; Gonado-somatic Index ; GSI ; Condition factor ; Biological characteristics ; Female ; Male ; Specimens ; Fisheries
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 39
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    facet.materialart.
    Unknown
    In:  http://aquaticcommons.org/id/eprint/22778 | 18721 | 2018-05-21 21:47:48 | 22778 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-10
    Description: In this study, three different age groups of male broodstocks (4, 5 and 6 years respectively) were used to fertilize eggs obtained from nine females. The results showed that 6 year old males had maximum body weight (1766 g), total length (56.3 cm) and sperm volume (31.83 ml). Results did not show significant difference in spermatocrit and spermatozoa concentration among age groups (p〉0.05). Our study showed maximum fertilization rate (98.5 %), survival rate until eyes pigmentation (91.17 %), hatching rate (94.5 %) and survival rate until absorption of yolk sack (97.16 %) for 4 years treatment group. Such positive relationships were detected between sperm production characteristics (spermatozoa concentration, spermatocrit and sperm volume) and fertilization parameters. Based on our results, it can be concluded that 4 year old males have high efficiency leading to fertilization success.
    Keywords: Aquaculture ; Biology ; Fisheries ; Age ; Male ; Artificial insemination ; Salmo trutta ; Biology ; Physiology ; Iran
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 328-335
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    facet.materialart.
    Unknown
    In:  http://aquaticcommons.org/id/eprint/23906 | 18721 | 2018-08-01 16:06:14 | 23906 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-15
    Description: During the fishing season, the statistical study on biological observation was carried out in four fishing stations located in the south west of the Caspian Sea. During the research activity 2806 stellate sturgeon were sampled. The result revealed that the ratio of stellate eggs weight used in processing of caviar were 20.7% of the total weight of the body. The number of females were more than males in the catch (77.8%). In 1991 the average length of females was 134.1 cm and the average weight with internal organs was 11.86 kg. But the mean length and weight in 1993 were 120.5 cm and 11.6 kg. The average age for female and male were estimated 12 and 10 years old respectively. Among the samples 92.7% of females were in the fourth stage of maturity and 60.4% of males were in third stage of maturity. In spite of the fact that during 1984-1991 fishing effort for catching Acipenser had been increased, yielding caviar had been decreased. This state was continued until 1994. So it was revealed that increasing fishing efforts wasn't led to increase the exploitation of Acipenser stocks.
    Keywords: Biology ; Female ; Male ; Caviar ; Weight ; Body ; Biological ; Fishing ; Eggs ; Acipenser stellatus ; SW Caspian Sea ; Caspian Sea ; Iran
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 49-64
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    facet.materialart.
    Unknown
    In:  http://aquaticcommons.org/id/eprint/23910 | 18721 | 2018-08-01 16:20:57 | 23910 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-15
    Description: Different length - weight relationship in 1000 male and 201 female of freshwater crayfish were studied and it was revealed that the length - length relationship is best described through linear regression, while weight - length relation is best described through a multimodel one. The "r" coefficient was over 90% in all cases. It was also shown that the average length of the females was more than the males, but the average weight of the males was more than the females. The percentage of males and females with total length more than 102 mm were 63.7% and 72.1% respectively.
    Keywords: Biology ; Length ; Weight ; Relationships ; Male ; Female ; Freshwater ; Astacus leptodactylus ; Crayfish ; Bandar Anzali ; Iran
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 9-18
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 11
    facet.materialart.
    Unknown
    In:  http://aquaticcommons.org/id/eprint/23941 | 18721 | 2018-08-01 17:58:17 | 23941 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-15
    Description: During a parasitological study on two Goby species, 15 Neogobius kesslerithe and 30 Neogobius fluviatilis caught in the South Caspian Sea and Tajan River (Mazandaran Province) respectively. The fish nematode Dichelyne minutus Rudalphi 1819 was isolated from 15 N kessleri and 2 N. fluviatilis. Both male and female specimen of this parasite, were observed in the intestine of 17 fishes, some of which had penetrated into the mucous membrane of the intestine. The infection rate in N. kessleri and N fluviatilis were 100% and 6.6% respectively.
    Keywords: Fisheries ; Health ; Nematoda ; Cucullanidae ; Neogobius fluviatilis ; Neogobius kessleri ; Goby ; Species ; Nematode ; Male ; Female ; Specimen ; Parasite ; Fishes ; Mucous ; Infection rate ; Dichelyne minutus ; Parasitological ; Caspian Sea ; Tajan River ; Mazandaran Province ; Iran
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 31-38
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 12
    facet.materialart.
    Unknown
    In:  http://aquaticcommons.org/id/eprint/23948 | 18721 | 2018-08-02 11:22:50 | 23948 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-15
    Description: Food habits and spawning season of Acanthopagrus latus (Sparidae) were studied in Bushehr, Delvar and Rostami waters of the Persian Gulf. Samples have been collected from March 1996 to February 1997 on a monthly basis. A total of 87 males and 95 females were examined and different biological parameters were measured. The Relative Length of the Gut (RLG) was estimated to be 0.64, which indicates that this is a carnivorous species. Food items have also been identified using numerical method. Out of 159 stomachs studied 36.36% were found to contain crabs, 33.99% other fish and 13.43% shrimps. The content of snails and sea urchins were 11/46% and 4/ 76% respectively. It is evident from the results of the study that A. latus feeds mainly on crabs and fish. The vacuity index was calculated to be 0.13. This indicated that this fish is an active predator. The Gonadosomatic Index (GSI) was estimated to be highest during February - March and lowest in June. GSI maxima was coincided with fecundity peak. The relationship between (GSI) and fish weight for females and males were r2=0.0235 and r2 =0.0214 respectively.
    Keywords: Biology ; Food Habits ; Spawning ; Acanthopagrus latus ; Sparidae ; Samples ; Male ; Female ; Length ; Gut ; RLG ; Species ; Numerical method ; Fish ; Shrimp ; Snail ; Sea urchins ; A. latus ; Feed ; Crab ; Vacuity index ; Gonado Somatic Index ; GSI ; Biological ; Delvar ; Bushehr ; Persian Gulf ; Iran
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 13-21
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 13
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25270 | 18721 | 2018-09-07 07:54:06 | 25270 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: Sampling of Astacus leptodactylusc were conducted in order to determination of biometrical and biological parameters suchas length, weight, sex ratio, fecundity and natural reproduction time. Two transect were selected at 49 34 and 49 36 geographical position on east Caspian Sea near to Anzali city. Metallic folding trap with Silurus glanis as attractive diet were used to catch Astacus leptodactylusc at each line the traps were set on depth of 35, 45, 55 and 65 (5 trap at each depth). Random sampling from each depth on tow lin for one year were conducted and the biometry performed on catched Astacus leptodactylusc where their sext uality and their ration were determined for eacd month , season and whole year. Absolute fecundity determined by cooking Astacus leptodactylusc , taking out the ovary weighing and counting them .Working fecundity assesed by separating eggs from their swiming leges while enomerate all egg . Complete randomized test of ANOVA for analysing the data were employed. The results showed average length and welght were calculated 122/07±1/74mm and 57/96±1/81gr respectively. Average absolute fecundity was 310/22 ±10/72 eggs , average working fecundity was 251/84±8/84 eggs, Average ovary weight was determined 4.31±0.619 gr and average number of eggs in one gr was 74/52±1/53 eggs. The sextual ratio in all year long was 1:1.32. The reproduction season is about seven month from Feburary to July and the moulting of males occurs two times each year. One of time is at May and the other is in September. The female molt thtina as the male start for second time.
    Keywords: Biology ; Iran ; Caspian Sea ; Bandar Anzali ; Biology ; Astacus leptodactylus eichwaldi ; Sex ratio ; Fecundity ; Silurus glanis ; ANOVA ; Female ; Male ; Coastal water
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 78
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 14
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25330 | 18721 | 2018-09-13 12:40:49 | 25330 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: Study of survey health management and diseases in hatcheries and fish farms can help us to knowledge and application control methods such as: prevention, treatment and increase high levels of production in hatchery and farms, finally. This survey carried out from 2005 to 2008 for 4 years in sturgeon hatcheries and farms of Golestan province. Sturgeon fishes include Huso Huso, Ship sturgeon, Acipenser persicus collected and for virology, bacteriology, fungius and hematology examined. Also, physicochemical parameters measured and recorded in different stages of culture. Results of this study showed that all of samples in virology was negative and did not observe any doubetful causes. In bacteriology CFU was variation from 3/9 ×105 to 6/9×10. The most parasites that detected in this survey was Cocolanus espherolanus, Sceria binopsulus semiarmatus and Amphilina fuliacea that separates from Acipenser Percicus, especially. The results about hematology parameters some important hematological indices of ship sturgeon include: The total RBC for female and mail specimens measured as 5.3±1.5 ×10^5, 4.8±0.5×10^5 per mm^3 respectively. The amount of haematocrit and hemoglobin for female and mail determined: 34.3±2.8, 35±1.4 percent and 10.3±0.9, 8.9±0.8 gr/dl .The MCV: 216.3± 96.2, 736.5± 102.5, MCH: 720.2±309.5, 186±0.7 and MCHC: 30±0.8, 25.5±3.4 percent respectively.The total WBC were (female, male): 21320±1054, 20580±777 per mm^3 and neutrophil: 16.4±2.5, 17±1.4 percent and lymphocyte: 74.4±2.4, 73.5± 0.7 percent and eosinophil: 6±1.4, 6.4±0.5 percent, monocyte: 2.8±0.8, 3.5±0.7 percent. There was not any significant differences (p〉0.05) between mentioned parameters in male and female (students t-test). Also evaluation of hematological parameters in bluga ( Huso huso) include: total RBC were (male , female) 5±0.3 ×105 , 4.9±0.6 ×105 per mm^3 ,respectively and hematocrit: 33.2±6.7 , 35.4±3.4 percent and hemoglobin: 11.2±1.5 , 12.2±1gr/dl and MCV: 669.9±172.2, 723.9±982.4 and MCH: 226.2±42.5, 249.5±35.4 and MCHC: 34.1±2.4, 34.6±3.6 percent respectively. The totals WBC were (male, female): 24800±707.1, 23042±1375.4 per mm^3 and neutrophil: 18.5±0.7, 21.4±1.1 percent and lymphocyte: 73.5±1.4, 68.4±1.1 percent and eosinophil: 5±2.8, 7±1.2 percent and monocyte: 3.5±3.5, 3.2±0.8 percent. According to statistically study the count of lymphocyte had significant difference between male and female fish and this count in male was higher than female. (p≥0.05).
    Keywords: Aquaculture ; Iran ; Golestan Province ; Mazandaran Province ; Guilan Province ; Fish ; Sturgeon ; Huso huso ; Ship ; Acipenser percicus ; Bacteriology ; Parasitology ; Health management ; Diseases ; Survey ; Aquaculture ; Hatcheries ; Samples ; Sceria binopsulus ; Amphilina fuliacea ; Female ; Male
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 395
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 15
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25182 | 18721 | 2018-09-03 17:06:03 | 25182 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: The biological aspects of Sepia pharaonis was studied during years 2006-07. The studied area restricted to the Bahrekan in Khouzestan province covering the depths of 2 up to 25m. The sampling methods were gillnet and bottom trawl. A total of 310 specimens collected, of which there wasn’t found any cuttlefish in the study area from July to October (5 months). The collected samples were transferred to the laboratory ashore for further biological measurements consist of: Mantle length, Body weight, sex determination. Gonado-Somatic Index, and determination of Spermatophoric Index, Spawning season, Food preference, Maturity stages and chemical analysis for food value determination. The results showed that the overall sex ratio is about M:F= 2:1 with percentage of 67.41% for males and 32.50% for females. Males are significantly bigger than females with average mantle length (ML) of 233.3 and 269.3 mm for female and male, respectively; with body weight of 1102.3 and 1450.6 g. The mantle length body weight relationship was found W=0.001 ML 2.540 (R2= 0.92) Female as: W= 0.0015 ML 4797 (R2= 0.93) male From point of feeding, the food preferences results indicated that fish is considered as main food, crabs as minor food and other marine organisms such as bivalvia and gastropods as random food. The highest vacuity Index (CV) and empty stomachs was determined for March-April and the lowest value was is December. Also, the maximum GSI was estimated for March-April months in which showing coherrances with the lowest food preference. The maximum spermatophoricfilaments were 856 and 45 for male pharaoh cuttlefish with mantle length of 300 and 185 mm, and on the other hand this values for fecundity were estimated 1589 and 53 for female specimens with 254 and 198 mm mantle length. The spawning season occurs in April- March in which accompany with migration of pharaoh cuttlefish towards shallow waters. The fishing season would be in this period in w.
    Keywords: Biology ; Iran ; Khouzestan province ; Bahrekan ; Sepia pharaonis ; Gillnet ; Sampling ; Specimens ; Weight ; Sex ; Gonado-somatic index ; Spawning ; Maturity ; Female ; Male ; Bivalvia ; Gastropods
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 85
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 16
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25127 | 18721 | 2018-08-26 13:33:35 | 25127 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: The present study was firstly conducted to study the rate of sexual maturity in Nereis diversicolor under suitable conditions of temperature and photoperiod. The second objective was to determine the potential of artificial breeding in these worms for mass culture. Nereis diversicolor worms were collected from the Anzali lagoon in 4000 sampling operations during the year’s 2004 to 2006 using Ekman grab with a surface area of 400 cm2. The water salinity, temperature and total organic matter (TOM) of sediments in the sampling region was recorded. The worms were maintained in 0.5 tons (1 x 1 m^2) tanks containing clayey-muddy sediment to a height of 20 cm covered with 10 cm water (5 ‰) until they reached a weight of 200-300 mg. Sexual maturity in this species was attained at 4-6 ºC and spawning occurred at approximately 16 ºC. The first gametes were observed five weeks after the temperature increased from 6 to 16 ºC. Sexual maturity was studied at various salinities (0.5, 5, 12, and 15 ‰). Results indicate that these worms attained earlier sexual maturity at salinity of 15 ‰, compared to other salinities studied. No significant differences (P〉0.05) were observed between sexual maturity attained at 12 ‰ and 15 ‰. Stocking density (20, 50, 100, 150 worms) was studied in terms of sex and showed that number of females were higher than males and the ratio was 11:1 (female: male). No significant differences (P〉0.05) were observed between the various stocking densities and their replicates. The effect of light and photoperiod in synchronizing reproduction in male and female N. diversicolor was studied. It was evident that reproduction behavior in adult worms increased for a period of one week at the end of each month after they are exposed to a prolonged photoperiod (L:D=16:8) followed by a period of dim light (simulated using 1 W lamps). Feeding trials were carried out with Saccharomyces cerevisiae, formulated fish diets and humus. Results showed that this diet was effective in speeding up sexual maturity in worms and significant effect of treatment was observed (P〈0.05) in worms fed a diet of humus alone. Eggs and sperms were fertilized and worms developed from the young monotrochophore with jelly layer to the trochophore larvae.
    Keywords: Biology ; Iran ; Anzali Lagoon ; Reproduction ; Sexual Maturity ; Fertilization ; Nereis Diversicolor ; Culture ; Salinity ; Temperature ; Spawning ; Female ; Male ; Larvae ; Sacchromyces cerevisiae ; Density
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 68
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 17
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25356 | 18721 | 2018-09-14 07:09:43 | 25356 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: This study was aimed to investigate the effects of different doses of two hormones and an anti-aromatase, i.e. 17a methyl testosterone (MT), methyl di hydrotestosterone (MDHT) or mestanolone and letozole in masculinization of Nile tilapia (Oreochromis niloticus) under the condition of brackish water in Bafgh station situated in Yazd province in center of Iran. Each experiment in this study was consisted of 5 treaments with 3 replicates each. A number of 1725 larvaes was distributed randomly among 15 replicates at the beginning of each experiment. Each experiment lasted 45 days and the larvaes were reared in aerated flow-through pots and fiberglass tanks filled with brackish water. The averages for temperature, salinity, pH and dissolved oxygen of water were 26.9 ê, 8 g/l, 7.6 and 5.78% respectively during this study. In experiment 1, three different doses of 40, 60 and 100 mg MT/k of feed were fed to different groups of 7 day post fertilization (dpf) larvaes for 45 days from the beginning of the experiment. The results showed that the larvaes in 40 mg group were 100 percent masculinized based on squash test performed at the end of the experiment but masculinization rates of those in 60 and 100 mg groups were 99.7 and 96.2 perecent respectively. Based on Dunkan test, total body length and weight averages measured in biometry 3 (at the end of the experiment) were not significantly different among groups but in biometry 2 (30 days after the beginning of experiment), they were significantly lesser only in 40 mg group (P〈0.05). There was significant differences in survival rate of different groups of larvaes in this experiment based on chi-square test (χ=31.166, P〈0.05) and the values in 40 and 100 mg groups (74.5 and 82.9% respectively) were lesser than those in 60 mg, control 1 and control 2 groups (84.3, 89.0 and 87.0 respectively). In experiment 2, masculinization rates of two different groups of larvaes immersed in 1800 µg MDHT/liter once in 10dpf and twice in 10 and 14dpf were 80.0 and 91.9 percent respectively. There were no significant differences in total body length and weight averages measured in biometry 2 between different groups but significant differences were observed in total body length only in biometry 3 (P〈0.05) where the highest values occurred in experiment 1 and control 1 groups and the lowest one in experiment 2. Significant differences observed in survival rate of different groups of larvaes in this experiment based on chi-square test (χ=15.165, P〈0.05) and the rates in experiment 1, control 2 and 3 groups (89.9, 86.4 and 89.9% respectively) were higher than those in experiment 2 and control 1 groups (82.0 and 82.3 respectively). In experiment 3, three different doses of anti-aromatse letrozole (200, 300 and 400 mg/k feed) were fed to different groups of 7 day post fertilization (dpf) larvaes for 45 days from the beginning of the experiment. The larvaes in 400 group .were all masculinized whereas the masculinization rates in 200 and 300 mg groups were 99.0 and 99.6% respectively. There were significant differences in total body length and weight averages measured in biometry 2 and 3 among groups in this experiment (P〈0.05) where the highest and the lowest values occurred in control 2 and experime2 groups respectively. Based on chi-square, the survival rate of different groups was significantly different (χ=41.119, P〈0.05) and the lowest rate occurred in experiment 2 group. No significant differences observed in gender ratios within all control groups in this study based on chi-square test. According to the findings acquired under the condition of brackish water at the present study, it would be potentially recommended to use MT and letrozole for the production of all male populations of Nile tilapia fish in order to provide fish farmers with no harmful environmental impacts on water sources in rivers and seas which occured due to the uncontroled breeding of tilapia. However, more research is needed to draw firm conclusions to use hormones and in especial anti-aromase letrozole because of the shortage of sufficient data in current references.
    Keywords: Aquaculture ; Iran ; Yazd province ; Bafgh ; Masculinization ; Nile tilapia ; 17α-methyl testosterone ; Methyl di hydro testosterone ; Mestanolone ; Body weight gain ; Total body lenght ; Brackish water ; Male ; Oreochromis niloticus ; Hormones ; Temperature ; Salinity ; pH ; Dissolved oxygen ; Fertilization ; Survival rate ; Larvae ; Investigation
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 61
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 18
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25404 | 18721 | 2018-09-20 12:28:18 | 25404 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: Population dynamics parameters and exploitation ratio of Jinga Shrimp, Metapenaeus affinis were studied from Sep 2011 to Dec 2011 and data collected from two landing places (Hendijan and Lifee-Bosif). During the project, more than 2200 specimens of jinga shrimp were measured. The mean value of length for the male and female were calculated as 9.8±0.86, 10.24±1.18 and mean value of weight for the male and female was as 6.730±1.64, 8.14±2.90 respectively. The length-weight relation were calculated as TW=0.024TL2.24 (n=1084,R^2=0.71) for males, TW=0.011TL2.80 (n=1081,R^2= 0.81) for females also we found significant different level length-weight relation in P〈0.05. The growth parameters of von Bertalanffy equation were as, L_∞: 14.73 and K: 1.1 and t0: -0.02. The estimated valve of total mortality, natural mortality, fishing mortality and exploitation ratio is Z: 4.35, M: 1.68, F: 2.67, E: 0.61 respectively. By using method analyses knife-edge selection, relative yield per recruitment (Y'/R) :0.014, relative biomass per recruitment, (B'/R) :0.085., Exploitation ratio maximum sustainable yield, Emax : 0.38; biological reference points for Jinga Shrimp stock was calculated. MSY and fmsy value was 600T and 46100day respectively. Result in this study showed exploitation ratio Jinga Shrimp stock is over fishing and decreases exploitation ratio proposed.
    Keywords: Aquaculture ; Iran ; Khuzestan province ; Jinga Shrimp ; Population ; Dynamics ; Exploitation ; Tiger tooth Croaker ; Otolithes ruber ; Metapenaeus affinis ; Population ; Male ; Female ; Mortality ; Coastal waters
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 202
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 19
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25184 | 18721 | 2018-09-03 17:16:24 | 25184 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: During last 65 years the catch of mullets had increasing trends with some fluctuations in the Iranian coastal water of the Caspian Sea .In this period about 138 thousand tons of mullets have been caught. Mullet’s account for 35% of total catch annually .In recent years species composition of mullets has chanched in the Iranian coastal water of the Caspian Sea and catch composition of golden grey mullet increased from 76% in 1995 to 98% in 2006. In this survey some biological characteristics of golden grey mullet have been studied in Iranian coastal water of the Caspian Sea .Fish samples have been gathered from commercial catch of beach seine cooperatives monthly in Iranian coastal water of the Caspian Sea over 2006 and 2007. In the laboratory fishes have been measured biometrically and biological parameters have been calculated .Also catch statistics of mullets during 2006-2007 have been obtained and discussed. Results showed that the catch of mullets in beach seine cooperatives during 2006 and 2007 was 4181 and 3685 tons respectively that golden grey mullet contribute 99% and 98% of the catch composition of mullets respectively. Length range of golden grey mullet caught by beach seine cooperatives was 19-50.2 cm with mean length of 32.7 ± 6.4 (± SD) and weight range was 67-1475 gr with mean weight of 411 ± 255 gr. The age structure of this species was comprised 2-10 years old fish with mean age of 4.42 years old. In this survey totally the sex ratio of male: female of golden grey mullet was 356: 434 that was significant variation from equal sex ratio. Pick of the spawning in Guilan province was in October and in Mazandaran and Golestan provinces was in November. In October the proportion of spawning females declined from western area (Guilan province) towards eastern parts (Golestan province).The highest proportion of spawning females was in December in Golestan province. The highest GSI index value was observed in September and October and it was decreased in November and December and it was consistent during January till April. The mean absolute fecundity was 700881±429987 eggs with minimum and maximum fecundity of 200112 and 2282862 eggs respectively. The Lm 50% for female golden grey mullet was calculated as 33.6 cm.
    Keywords: Biology ; Iran ; Caspian Sea ; Golestan province ; Guilan province ; Golden grey mullet ; Liza aurata ; Species ; Survey ; Samples ; Male ; Female ; Sex ratio ; Spawning ; GSI ; Fecundity ; Coastal waters
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 56
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 20
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25202 | 18721 | 2018-09-05 16:22:51 | 25202 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: The Kutum, Rutilus frisii kutum, is one of the most important bony fishes in Iranian coastal of Caspian Sea. Its harvest range is between 9000-10000 tons in a year, nearly 60% of the income of Bony fish fishery produced by kutum fishery. The stock of this species reduced drastically in 1982 and the catch slumped to the less than 250 tons in a year. Kutum spawning grounds deterioration, illegal catch, and lack of restocking program were the main cause of the decline. This Spices in nature comprised by two distinct form, autumn and spring form. It is worth to be mentioned, by the effect of Caspian Sea Bony fishes Research Center s experts in 1983, artificial spawning and releasing the fries to the sea were commenced and the catch steadily improved. But all activities concerning restocking of kutum concentrated in spring form, as at present about 260 million its fries are released into sea for restocking by Iranian Fisheries Organization, but for above reasons and lack of restocking program, the populations of autumn form gravely shrinked and neared to be extinct. Therefore, to enhance the biodiversity and boost fishers livelihood of kutum in Caspian Sea this project implemented by cooperation of Iranian Fisheries Organization (IFRO) and Caspian Environment Program (CEP) in Aquaculture Institute (Inland Waters). In this project, brooders caught from Anzali lagoon and maintained in two different condition, include of floating cages in Anzali lagoon and earthen ponds in Sefidrud Fisheries Research Station. The results showed that there weren’t significant differences between two maintenance statuses in maturation period and other reproductive characteristics of brooders. The ratio of male to female was 1 to 1.4. Minimum and maximum weight measured 1450 to 3100 g (with average of 1850 g) in female and 670 to 1900 g (with average of 1165 g) in male, respectively. The first natural spawning of brooders occurred in the end of January in temperature of 8 till 10 °C in concrete ponds. Also, some of maintained brooders in earthen ponds spawned in February. The average number of absolute, function and relative fecundity determined 88565 16809, 73805 14008 and 48670 12056, respectively. For artificial spawning, male and female brooders injected by pituitary gland with dose of 2-3 and 4-5 mg/kg body weight, respectively. Approximately, 10 and 8 present of female were over-ripe and immature in March (artificial spawning time), respectively. More than 59 % of injected female brooders induced to spawning in first stage after 10-12 hours and 13 % of them in twice stage and 7-8 hours after first stage. And also, 27.6% of females didn’t positive response to injection. Dry method used for eggs fecundity and incubation period lasted 7- 10 days in 14-16 °C. In totally, eggs fertilization were more than 95% and the average of eggs fertilization percent in throughout of period measured more than 92.7 6 %. Eyed eggs appearance occurred 3 days after fecundity and its mean was 92.7 15.1%. Larvae after yolk sac absorption feed with dry milk for 4-5 days and then introduced into fertilized earthen ponds (500 m2 and equipped to aerators) in intensive condition and fed with micro pellet food for 3-4 month. In finally, more than 1.8 million fries of 1-2 g and some more than 5 g produced and released into Anzali lagoon to its restocking for first time. It is expected that continuing of restocking process of autumn form kutum by Iranian Fisheries Organization eventuate to population increasing of this form in Caspian Sea in future.
    Keywords: Aquaculture ; Iran ; Caspian Sea ; Anzali Lagoon ; Sefidrud River ; Artificial propagation ; Culture ; Rutilus frisii kutum ; Kutum ; Bony Fish ; Fishery ; Spawning ; Biodiversity ; Aquaculture ; Brooders ; Fecundity ; Male ; Female ; Population
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 79
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 21
    facet.materialart.
    Unknown
    In:  http://aquaticcommons.org/id/eprint/25928 | 18721 | 2018-11-22 07:18:23 | 25928 | Khorramshahr University of Marine Science and Technology
    Publication Date: 2021-07-16
    Description: Conservation of genetic diversity of juveniles used for restocking of natural populations requires serious attention in artificial breeding protocol of the Caspian brown trout Salmo trutta caspius. Unbalanced contribution of male and female breeders to progeny in present artificial breeding has resulted in the reduction of effective population size in breeders. Equalization of milt volume did not also result in balanced contribution of breeders. With regard to the possible effect of sperm concentration on contribution of breeders to production of progeny, effective population size in breeders and genetic diversity of progeny were determined in mixed milt fertilization of 6 male and 2 female breeders with equal sperm concentration and ova number. Parentage assignment was performed using exclusion method in FAP program by analyzing 9 microsatellite loci and choosing the 3 most polymorphic ones, Str 58, Str 73 and Str 591, in breeders. More than 91% of progeny were assigned to their parents. Effective population size was calculated as 5.24 (0.65) and the number of alleles and expected heterozygosity decreased in progeny (6.67 and 0.726 ± 0.011) compared to parents (7.33 and 0.808) significantly (P〉0.05). In conclusion, equalization of sperm concentration of male breeders did not result in the balanced contribution of male breeders to ova fertilization and production of progeny in mixed milt fertilization of Caspian brown trout and genetic diversity of progeny remained significantly decreased.
    Keywords: Biology ; Iran ; Equalization ; Sperm ; Concentration ; Male ; Salmo trutta caspius ; Fertilization ; Genetic ; Diversity ; Progeny
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 45-57
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 22
    facet.materialart.
    Unknown
    In:  http://aquaticcommons.org/id/eprint/25929 | 18721 | 2018-11-22 06:49:55 | 25929 | Khorramshahr University of Marine Science and Technology
    Publication Date: 2021-07-16
    Description: The crude protein content and amino acid compositions of muscle from wild and cultured of male and female Acanthopagrus latus were determined by HPLC. There were quantitative differences between individual amino acids in the tissues investigated, depending on the sex and location. It was noted that, among all the samples studied in tissues, sexes and locations, lysine and isoleucine were the principal essential amino acid (EAA) and glutamic acid was mainly for non-essential amino acid (NEAA). Lysine and isoleucine of male muscles had a significantly higher (P〈0.05) amount than female muscles. The crude protein content in male and female muscles was not found to be significantly different. Depending on location, the percentages of arginine, leucine, isoleucine, lysine, serine, glycine, alanine and tyrosine were significantly different (P〈0.05) in muscles of wild and cultured fish. The wild seabream possessed considerably higher protein content than cultured seabream muscle. The results showed that wild male fish muscle contained a higher (P〉0.05) level of EAA than other groups. The results indicate that the Acanthopagrus latus is a healthful component of the human diet.
    Keywords: Aquaculture ; Biology ; Iran ; Amino acid ; Composition ; Muscle ; Male ; Female ; Acanthopagrus latus ; NEAA ; Protein
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 58-66
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 23
    facet.materialart.
    Unknown
    Iranian Fisheries Science Research Institute | Tehran, Iran
    In:  http://aquaticcommons.org/id/eprint/25801 | 18721 | 2018-10-13 08:37:23 | 25801 | Iranian Fisheries Science Research Institute
    Publication Date: 2021-07-16
    Description: Due to the usefulness of shrimp broodstock pelleted diets, from aspects of, easier maintenance, transportation, broodstock feeding, and cheaper as compared to natural wet diets, the use of natural wet foods, include sand worm (Perinereis nuntica), cattle fish )Sepia pharaonis) and veal livier decreased and the quantity of pelleted diet increased. Survey was conducted, in tankes with a volume of 300 liters. Tanks were filled with 150 liters of water. 10 broodstock in each tank was left, with an average weight of 37±2 grams. Daily feeding rate, was twenty-five percent of their biomass. The survey was include, 9 treatments with 3 replicates in each tank as described below. Control treatment: broodstock feeding only with, sand worm (33%), cattle fish (34%) and bull livier (33%). Exprimental treatment 1: broodstock feeding with pelleted diet contain 50 percent crude protein and 8 percent crude fat (50%)+sand worm (16 %)+cattle fish (18%)+veal livier (16%). Treatment 2: broodstock feeding with pelleted diet contain 50 percent crude protein and 10 percent crude fat (50 %)+sand worm (16 %)+cattle fish (18%) and veal livier (16%). Treatment 3: broodstock feeding with pelleted diet contain 40 percent crude protein and 10 percent crude fat (50%)+sand worm (16 %)+cattle fish (18 %) and veal livier (16 %). Treatment 4: broodstock feeding with pelleted diet contain 40 percent crude protein and 8 percent crude fat (50 %)+sand worm (16 %)+cattle fish (18 %) and veal livier (16 %). Treatment 5: broodstock feeding with pelleted diet contain 50 percent crude protein and 10 percent crude fat (100 %). Treatment 6: broodstock feeding with pelleted diet contain 50 percent crude protein and 8 percent crude fat (100 %). Treatment 7: broodstock feeding with pelleted diet contain 40 percent crude protein and 10 percent crude fat (100 %). Treatment 8: broodstock feeding with pelleted diet contain 40 percent crude protein and 8 percent crude fat (100%). The results showed that, Gonadosomatic index (GSI) in treatments 3: control and 6, was significantly more than others treatments (p〈0.05). Hepatosomatic indexes, in often treatments was almost equal, and in some cases were significantly different (p〈0.05). In treatments 3 and control, absolute fecundity, was significantly more than others treatment (p〈0.05). The survival percent, in treatment 8 was significantly less than others treatments (p〈0.05). The survival percent in others treatments was not significantly difference (p〉0.05). From the aspect of mean weight of broodstock, wasn’t significant difference in treatments (p〉0.05). From the aspect of mean length of carapac, wasn’t significant difference in treatments (p〉0.05). From the aspect of mean body length, wasn’t significant difference in often treatments (p〉0.05), and in treatments 5 and 6 was significantly less than others (p〈0.05). In the determination of relasheship between kind of treatments and abundance of maturated broodsock, wasn’t significantly difference (p〉0.05). In the determination of, correlation between weight (g) and total length(cm), (r=0.71), weight and carapace length (cm) (r=0.70), the correlation was strong. Between GSI, HIS, carapace length and total length the correlation was intermediate (r=0.54). The correlation between absolutely fecundity and total length (r=0.20), absolutely fecundity and carapace length (r=0.28), absolutely fecundity and weight (r=0.35) was weak. The results showed that, the use of combination of pelleted diet and natural wet diets can increase female maturation indexes. Totally we can noted that, GSI, HIS and absolute fecundity of broodstock, that fed with pelleted diet contain 40 percent crude protein and 10 percent crude fat (50 %)+sand worm (16 %)+cattle fish (18 %) and veal livier (16 %) (treatment 3) was better than the other treatments. Positive effects of this treatnent on sexual indexes, was due to provide part of nutritional requirement of shrimp broodstock from pelleted diet.
    Keywords: Aquaculture ; Iran ; Natural wet diet ; Pelleted diets ; Maturation ; Male ; Female ; Western white shrimp ; Artifitial diets ; Broodstock ; Litopenaeus vannamei
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 38
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 24
    Publication Date: 2020-09-30
    Description: This work focuses on the observation of data recorded by the seismic temporary network installed in the Amatrice area, under the umbrella of the Italian Center for Seismic Microzonation (http://www.centromicrozonazionesismica.it), following the M 6.0 earthquake of August 24, 2016 in Central Italy. The aim was studying the presence of an evident late low frequency wave packet observed in some of the recorded aftershocks. In order to interpret this phenomenon, we combined a beam-forming analysis performed on these data with the statistics on residuals of localizations related to the same events, recorded by the Italian Seismic Network (RSN). The total number of analyzed events, characterized by M≥=3 and epicentral distances between 30 and 55 Km, is 356. By observing the seismic traces of these events there was an evidence, in some of them, of a low frequency packet appearing 10 seconds after the first arrival. The evidence of this packet was correlated with epicentral distance and focal depth. For a subset of stations, considered as an array, a beam-forming analysis was performed by using the ObsPy toolbox (M. Beyreuther et al., 2010). Results of this analysis gave information in terms of slowness and azimuth to distinguish the main seismic phases of the considered events. In addition, by using locations of the RSN records (Chiaraluce et al., 2017), we performed a parallel analysis within the subset of events with clear evidence of the low frequency packet. We relocated these events by using the NonLinLoc code, with a fixed 1D P-wave velocity model, and varying the Vp/ Vs ratio in the range 1.6–2.0. We found that the P phases residuals are not influenced by the Vp/Vs ratio changes whereas the higher the Vp/Vs the lower are the S phases residuals. Higher values of Vp/Vs ratio, fixing Vp values, could mean a decrease of Vs connected to particular effects during the seismic waves path, that are probably due to geological heterogeneities at local or larger scale
    Description: Published
    Description: Miami, Florida
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Keywords: Microzonation ; Seismology ; Wave propagation ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 25
    Publication Date: 2020-09-30
    Description: Following the M 6.0 of August 24 2016 Amatrice earthquake, a temporary seismic network was installed in the village of Amatrice, under the umbrella of the Italian Center for Seismic Microzonation (http://www.centromicrozonazionesismica.it), who conducted a preparatory survey to seismic microzonation with other Italian Institutions. This work focuses on data analysis of 7 stations installed in the Amatrice terrace which is representative of the geological condition of the town, with the aim of studying the possible presence of secondary effects during the seismic sequence caused by site conditions. Stiff bedrock outcroppings were also sampled with 2 reference stations. Preliminary analyses carried out on several earthquakes with Ml 〉 4 highlight the presence of a low frequency phase with a high energy content at 6 -7 seconds after the first P-wave arrival in almost all the recordings. This wave package was observed for the Mw 6.5 of October 30 earthquake and it has the highest amplitude of the entire recordings, having PGA values of 0.5 g and frequency between 2 and 3 Hz. Frequency-wavenumber analysis performed for the 7 stations array gives an important contribution for the interpretation of this phenomenon, showing that the low frequency wave-package for the examined events does not always show back-azimuth and slowness values compatible with the very first portion of the seismic record. It could be associated to the presence of reflected or refracted waves generated by secondary effects as geological or morphological heterogeneities at local or larger scale.
    Description: Published
    Description: Vienna
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Keywords: Microzonation ; Seismology ; Wave propagation ; Seismic amplification ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 26
    Publication Date: 2020-11-30
    Description: Normal fault systems, outcropping or hidden below Quaternary covers in intermountain basins, are the expression of the Neogene-Quaternary evolution of central Italy, characterized by an extensional tectonic regime following the fold and thrust structuring of the Appenninic orogen. The presence of these features plays an important role in seismic risk evaluation of an area. In this work we deal with the use of single-station seismic noise measurements to detect sudden lateral variations of the geometries and/or properties of subsoil connected to the presence of tectonic elements (fault zones). Ambient noise data were collected along transects perpendicular to the strike of hypothetical fault lines for 3 test sites within the Abruzzi Region. The proposed approach is suitable for detecting in a fast and simple way local lateral changes in the subsoil characteristics close to geological structures and can be very effective to properly address more expensive and time consuming classical geophysical and paleoseismological approaches.
    Description: Published
    Description: Pescina, Fucino Basin, Italy
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Keywords: Microzonation ; Seismology ; Applied geophysics ; Detection of buried geological structures ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 27
    Publication Date: 2020-09-30
    Description: In this work we tested the capability of single station ambient noise spectral ratios (HVNSR) technique to be used as a proxy for detecting sharp variations in the subsoil characteristics in sedimentary basins. In sites characterized by 1D response HVNSR is able to detect the resonance frequency of sediments (f0) to be related with their thickness and velocity. In quasi-1D geological situation, a smooth variation in the resonance frequency suggests some variation in the thickness of the soft sedimentary layers or in their velocity. In the case of sharp lateral variation of the subsoil, as in presence of morphological steps or buried faults in the bedrock, the noise wave-field becomes more complex and spectral ratios show some directional effect strictly related to the presence of the lateral heterogeneity (Matsushima et al. 2014). In this work we focus our attention on the detection of a buried shallow tectonic element known in bibliography (Galadini, Galli 1999) as the Luco dei Marsi fault, located in the western margin of the Fucino basin (central Appenines, Italy). We performed simultaneous ambient noise measurements using MarsLite digitizers equipped with Lennarts 3d-5s velocimeters along a transect, with inter-station distance between 30 and 50 meters, which crosses perpendicularly the surface projection of fault line. The collected data, analyzed with classical HVNSR technique, show some complexities in the f0 distribution compatible with the presence of the buried fault. In detail, our results highlight a 1D response with a clear resonance peak for the stations located away from the fault. Moving closer to the fault line, where the 1D condition is not verified, the resonance peak becomes broader. Directional analysis of spectral ratios suggests the dependence of the noise wave-field to the presence of the fault line. Close to the geological feature, results of directional analysis show a doubling in the resonance frequency with relative amplitudes changing for fault-parallel and fault-normal direction of polarization. To support with an independent approach our observations, an electrical resistivity tomography was performed along the transect whose results show the presence of a clear step in a high resistivity shallow layer that can be assumed as the bedrock. After this analysis we decided to extend the ambient noise transect towards the centre of the basin where no fault line is mapped and where we expected a smooth lowering of f0 values due to the deepening of the bedrock. This feature was really observed for a while but at a distance between 400 and 500 meters from the Luco fault we detected again some anomaly in HVNSR data with a doubling of resonance frequency and relative amplitudes depending from the direction of polarization. This observation suggests the presence of deeper tectonic element parallel to the Luco fault. As a conclusion of our work we believe that HVNSR and polarization analysis can represent a quick and fast method to hypothesize the presence of buried discontinuity in the subsoil and can be usefully used to guide the positioning of more sophisticated geophysical analysis aimed at mapping their geometries.
    Description: Published
    Description: Trieste, Italy
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Keywords: Microzonation ; Seismology ; Applied geophysics ; Detection of buried geological structures ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 28
    Publication Date: 2014-12-13
    Description: Current earthquake early warning (EEW) systems lack the ability to appropriately handle multiple concurrent earthquakes, which led to many false alarms during the 2011 Tohoku earthquake sequence in Japan. This paper uses a Bayesian probabilistic approach to handle multiple concurrent events for EEW. We implement the theory using a two-step algorithm. First, an efficient approximate Bayesian model class selection scheme is used to estimate the number of concurrent events. Then, the Rao-Blackwellized Importance Sampling method with a sequential proposal probability density function is used to estimate the earthquake parameters, that is hypocentre location, origin time, magnitude and local seismic intensity. A real data example based on 2 months data (2011 March 9–April 30) around the time of the 2011 M 9 Tohoku earthquake is studied to verify the proposed algorithm. Our algorithm results in over 90 per cent reduction in the number of incorrect warnings compared to the existing EEW system operating in Japan.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 29
    Publication Date: 2014-11-07
    Description: Fractured rocks are known to exhibit seismic anisotropy and shear wave splitting (SWS). SWS is commonly used for fractured rock characterization and has been shown to be sensitive to fluid type. The presence of partial liquid/gas saturation is also known to affect the elastic properties of rocks. The combined effect of both fractures and partial liquid/gas saturation is still unknown. Using synthetic, silica-cemented sandstones with aligned penny-shaped voids, we conducted laboratory ultrasonic experiments to investigate the effect fractures aligned at an oblique angle to wave propagation would have on SWS under partial liquid/gas saturation conditions. The result for the fractured rock shows a saturation dependence which can be explained by combining a fractured rock model and a partial saturation model. At high to full water saturation values, SWS decreases as a result of the fluid bulk modulus effect on the quasi-shear wave. This bulk modulus effect is frequency dependent as a result of wave-induced fluid flow mechanisms, which would in turn lead to frequency dependent SWS. This result suggests the possible use of SWS for discriminating between full liquid saturation and partial liquid/gas saturation.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 30
    Publication Date: 2014-11-07
    Description: The effect of network density and geometric distribution on kinematic non-linear source inversion is investigated by inverting synthetic ground motions from a buried strike-slip fault ( M w 6.5), that have been generated by dynamic spontaneous rupture modelling. For the inversion, we use a physics-based regularized Yoffe function as slip velocity function. We test three different cases of station network geometry: (i) single station, varying azimuth and epicentral distance; (ii) multistation circular configurations, that is stations at similar distances from the fault, and regularly spaced around the fault; (iii) irregular multistation configurations using different numbers of stations. Our results show: (1) single station tests suggest that it may be possible to obtain a relatively good source model even using a single station. The best source model using a single station is obtained with stations at which amplitude ratios between three components are not large. We infer that both azimuthal angle and source-to-station distance play an important role in the design of optimal seismic network for source inversion. (2) Multistation tests show that the quality of the inverted source systematically correlates neither with the number of stations, nor with waveform misfit. (3) Waveform misfit has a direct correlation with the number of stations, resulting in overfitting the observed data without any systematic improvement of the source. It suggests that the best source model is not necessarily derived from the model with minimum waveform misfit. (4) A seismic network with a small number of well-spaced stations around the fault may be sufficient to obtain acceptable source inversion.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 31
    Publication Date: 2014-09-20
    Description: The Maule earthquake (2010 February 27, M w 8.8, Chile) broke the subduction megathrust along a previously locked segment. Based on an international aftershock deployment, catalogues of precisely located aftershocks have become available. Using 23 well-located aftershocks, we calibrate the classic teleseismic backprojection procedure to map the high-frequency seismic radiation emitted during the earthquake. The calibration corrects traveltimes in a standard earth model both with a static term specific to each station, and a ‘dynamic’ term specific to each combination of grid point and station. The second term has been interpolated over the whole slipping area by kriging, and is about an order of magnitude smaller than the static term. This procedure ensures that the teleseismic images of rupture development are properly located with respect to aftershocks recorded with local networks and does not depend on accurate hypocentre location of the main shock. We track a bilateral rupture propagation lasting ~160 s, with its dominant branch rupturing northeastwards at about 3 km s –1 . The area of maximum energy emission is offset from the maximum coseismic slip but matches the zone where most plate interface aftershocks occur. Along dip, energy is preferentially released from two disconnected interface belts, and a distinct jump from the shallower belt to the deeper one is visible after about 20 s from the onset. However, both belts keep on being active until the end of the rupture. These belts approximately match the position of the interface aftershocks, which are split into two clusters of events at different depths, thus suggesting the existence of a repeated transition from stick-slip to creeping frictional regime.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 32
    Publication Date: 2014-10-08
    Description: Geophysical and geological data suggest that Tibetan middle crust is a partially molten, mechanically weak layer, but it is debated whether this low-viscosity layer is present beneath the entire plateau, what its properties are, how it deforms, and what role it has played in the plateau's evolution. Broad-band seismic surface waves yield resolution in the entire depth range of the Tibetan crust and can be used to constrain its shear-wave velocity structure (indicative of crustal composition, temperature and partial melting) and radial anisotropy (indicative of the patterns of deformation). We measured Love- and Rayleigh-wave phase-velocity curves in broad period ranges (up to 7–200 s) for a few tens of pairs and groups of stations across Tibet, combining, in each case, hundreds of interstation measurements, made with cross-correlation and waveform-inversion methods. Shear-velocity profiles were then determined by extensive series of non-linear inversions of the data, designed to constrain the depth-dependent ranges of isotropic-average shear speeds and radial anisotropy. Shear wave speeds within the Tibetan middle crust are anomalously low and, also, show strong lateral variations across the plateau. The lowest mid-crustal shear speeds are found in the north and west of the plateau (~3.1–3.2 km s –1 ), within a pronounced low-velocity zone. In southeastern Tibet, crustal shear wave speeds increase gradually towards southeast, whereas in the north, the change across the Kunlun Fault is relatively sharp. The lateral variations of shear speeds within the crust are indicative of those in temperature. A mid-crustal temperature of 800 °C, reported previously, can account for the low shear velocities across Lhasa. In the north, the temperature is higher and exceeds the solidus, resulting in partial melting that we estimate at 3–6 per cent. Strong radial anisotropy is required by the data in western-central Tibet (〉5 per cent) but not in northeastern Tibet. The amplitude of radial anisotropy in the crust does not correlate with isotropic-average shear speed (and, by inference, with crustal rock viscosity) or with surface elevation. Instead, radial anisotropy is related to the deformation pattern and is the strongest in regions experiencing extension (crustal flattening), as noted previously. The growth of Tibet by the addition of Indian crustal rocks into its crust from the south is reflected in the higher crustal seismic velocities (and, thus, lower temperatures) in the southern compared to northern parts of the plateau (more recently added rocks having had less time to undergo radioactive heating within the thickened Tibetan crust). Gravity-driven flattening—the basic cause of extension and normal faulting in the southern, western and central Tibet—is evidenced by pervasive radial anisotropy in the middle crust beneath the regions undergoing extension; the overall eastward flow of the crust is directed by the boundaries and motions of the lithospheric blocks that surround Tibet.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 33
    Publication Date: 2014-10-08
    Description: The aseismic Murray ridge (MR) is a continuation of the Owen fracture zone which marks the boundary between the Indian and Arabian plates. Due to large variation in morphology and structure within this NE–SW trending ridge in the Arabian Sea a large variation of the bathymetry from few hundred metres to about 4000 m is seen. Observed seismicity on the ridge system is predominantly strike-slip. Tsunamis generated in the Makran subduction zone (MSZ) will propagate through the MR system due to its proximity. As the tsunami speed depends on the depth of the ocean, bathymetry plays a vital role on tsunami propagation. In this paper, the effect of tsunami propagation through the MR system is carried out with the existing bathymetry and comparing the results by removing the bathymetry. To study this phenomenon the 1945 Makran tsunami and worst possible tsunamigenic earthquakes form eastern and western MSZ are considered. The directivity of tsunami propagation with the ridge system is seen to change after crossing the MR towards the southeast direction for tsunamis generated in the eastern MSZ. For tsunami generated in the western MSZ there is no change in its directivity and is almost same as without the ridge with propagation being towards the open sea. Hence the MR not only affects the amplitude of the tsunamis but also the directionality and the arrival times.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 34
    Publication Date: 2014-10-08
    Description: The effects of Earth's layered structure, gravity and curvature on coseismic deformation are systematically quantified for all fundamental point sources and some finite-fault sources, respectively. The point-source simulations show that the layering effect (about ≤25 per cent) is significantly higher than the gravity effect (about ≤11 per cent) and the curvature effect (about ≤5 per cent). A case study on the 2011 M w 9.0 Tohoku earthquake is made to quantify the uncertainties of the dislocation models of large earthquakes, in which the three different effects are neglected. Finally, it is investigated how geodetic finite-fault slip inversions are affected by neglecting the layering effect.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 35
    Publication Date: 2014-10-08
    Description: Multichannel analysis of surface waves (MASW) method analyses high-frequency surface waves to determine shear ( S )-wave velocities of near-surface materials, which are usually unconsolidated and possess higher Poisson's ratios. One of key steps using the MASW method to obtain the near-surface S -wave velocities is to pick correct phase velocities in dispersive images. A high-frequency seismic survey conducted over near-surface materials with a higher Poisson's ratio will often result in data that contains non-geometric wave, which will raise an additional energy in the dispersion image. Failure to identify it may result in misidentification. In this paper, we have presented a description about leaky surface wave and the influence caused by the existence of leaky waves in a high-frequency seismic record. We first introduce leaky wave and non-geometric wave. Next, we use two synthetic tests to demonstrate that non-geometric wave is leaky wave and show the properties about leaky surface wave by eigenfunctions using Chen's algorithm. We show that misidentification may occur in picking the dispersion curves of normal Rayleigh wave modes because the leaky-wave energy normally connects energy of fundamental and/or higher modes. Meanwhile, we use a real-world example to demonstrate the influence of leaky wave. We also propose that muting and filtering should been applied to raw seismic records prior to generating dispersive images to prevent misidentifying leaky surface waves as modal surface waves by a real-world example. Finally, we use a three-layer model with a low-velocity half-space to illustrate that leaky surface waves appear on condition that the phase velocities are higher than maximum S -wave velocity of the earth model when solving the Rayleigh equation.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 36
    Publication Date: 2014-10-23
    Description: Recent studies have shown that many early aftershocks are missing in the regular earthquake catalogues immediately following a moderate to large earthquake. An effective way to recover those missing aftershocks is to use existing events as templates to scan through continuous waveforms to detect additional events, also known as the matched filter technique. Here, we use this technique to detect missing early aftershocks within 3 d after the 2010 M L 6.4 Jiashian earthquake in southern Taiwan. Using waveforms of 875 aftershocks listed in the Central Weather Bureau catalogue as templates, we have detected 2307 early aftershocks in the first 3 d following the main shock. The aftershock rate generally follows an Omori's type decay with a logarithmic slope p of ~0.8. In addition, aftershocks migrated along the northwestward direction with a velocity of ~6–7 km decade –1 and ~3–4 km decade –1 in the opposite direction in depth of 0–20 km. Regions with different seismic properties in the vicinity of the main shock hypocentre may affect the locations and migration patterns of the early aftershocks. We also found a spatial anticorrelation between the main shock slip and aftershock hypocentres in first half hour, although aftershocks at later times filled in regions with moderate amount of slips during the main shock.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 37
    Publication Date: 2014-10-23
    Description: We present a 3-D model of P and S velocities beneath El Hierro Island, constructed using the traveltime data of more than 13 000 local earthquakes recorded by the Instituto Geográfico Nacional (IGN, Spain) in the period from 2011 July to 2012 September. The velocity models were performed using the LOTOS code for iterative passive source tomography. The results of inversion were thoroughly verified using different resolution and robustness tests. The results reveal that the majority of the onshore area of El Hierro is associated with a high-velocity anomaly observed down to 10–12-km depth. This anomaly is interpreted as the accumulation of solid igneous rocks erupted during the last 1 Myr and intrusive magmatic bodies. Below this high-velocity pattern, we observe a low-velocity anomaly, interpreted as a batch of magma coming from the mantle located beneath El Hierro. The boundary between the low- and high-velocity anomalies is marked by a prominent seismicity cluster, thought to represent anomalous stresses due to the interaction of the batch of magma with crust material. The areas of recent eruptions, Orchilla and La Restinga, are associated with low-velocity anomalies surrounding the main high-velocity block. These eruptions took place around the island where the crust is much weaker than the onshore area and where the melted material cannot penetrate. These results put constraints on the geological model that could explain the origin of the volcanism in oceanic islands, such as in the Canaries, which is not yet clearly understood.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 38
    Publication Date: 2014-10-23
    Description: The b value of the Gutenberg–Richter (GR) distribution is estimated as a function of a threshold magnitude m th and it is found to depend on m th for magnitudes larger than the completeness magnitude m c . We identify a magnitude interval [ m c , m m ] where b is a decreasing function of m th followed by a regime of increasing b for large magnitudes. This is a common feature of experimental catalogues for different geographic areas. The increase at large m th is explained in terms of an upper magnitude cut-off in experimental catalogues due to finite size effects. We develop a rigorous mathematical framework to relate the decrease of b in the intermediate regime to the functional form of the distribution of the b values. We propose two hypotheses: The first is that the spatial and temporal variability of b leads to a b distribution peaked around its average value. The second is that main shocks and aftershocks are distributed according to the GR law with different b values, leading to a bimodal distribution of b . Simulated Epidemic Type Aftershock Sequences catalogues, generated according to this hypothesis, exhibit the same magnitude distribution of experimental ones. In alternative, we cannot exclude the b dependence on m caused by magnitudes not homogeneously evaluated in a seismic catalogue. In the latter scenario our results provide the correction terms to the estimated magnitudes.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 39
    Publication Date: 2014-11-02
    Description: Continental China consists of a complex amalgamation of geotectonic units and has experienced strong and widespread tectonic deformation since the Mesozoic. To understand its geological structure better, we conducted a systematic receiver function analysis using a total of 83 509 teleseismic traces in the time period of 2009–2010 recorded by 798 broad-band stations, among which 749 stations are permanent digital seismic stations from China Earthquake Networks Center and 49 stations were temporarily deployed in northern Central Tibet. A standard H – stacking method is employed to determine Moho depth and V p / V s ratio underneath each station from teleseismic receiver function analysis. The obtained Moho depth variations are generally consistent with those determined from various deep seismic soundings profiles. We combine our results with those from previous receiver functions studies to produce a high-resolution map of Moho depth and V p / V s variation for continental China. Compared to previous studies, the new study concerns many more stations and the resulting Moho depth map has much higher lateral resolution, especially in the eastern China. Overall, the Moho depth variation has a remarkable correlation with major tectonic units in continental China. For example, across the well-known gravity gradient line in east China, there is a clear shift in Moho depths. In general, the map of V p / V s ratio shows relatively high anomalies underneath Tibetan Plateau, along the gravity gradient line, and under several volcanoes.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 40
    Publication Date: 2014-10-23
    Description: In this study, information carried by the ambient seismic field is exploited to extract impulse response functions between two seismic stations using one as a ‘virtual’ source. Interferometry by deconvolution method is used and validated by comparing the extracted ambient noise impulse response waveforms with records of moderate magnitude earthquakes (from M w 4 to 5.8) that occurred close to the virtual source station in Japan. As the information is only available at low frequencies (less than 0.25 Hz), the ambient seismic field approach is coupled to a non-stationary stochastic model to simulate time domain accelerograms up to 50 Hz. This coupling allows the predicted ground motion to have both the deterministic part at low frequencies coming from the source and the crust structure and the high-frequency random contribution from the seismic waves scattering. The resulting combined accelerograms for an M w 5.8 event show a good agreement with observed ground motions from a real earthquake.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 41
    Publication Date: 2014-11-02
    Description: By relocation of shallow and intermediate depth earthquakes and joint evaluation of already available and properly estimated waveform inversion focal mechanisms we investigate the location and shallow kinematics of the residual subducting slab in the Calabrian Arc region, that is the only, apparently still active segment of the old subduction front of the western Mediterranean. In agreement with high P -wave velocity anomaly found at intermediate depths by previous local earthquake tomography, our shallow-to-intermediate earthquake hypocentre distribution shows that the Ionian subducting slab is still in-depth continuous only in a small internal segment of the Arc, while detachment or break-off processes have already developed elsewhere along the Arc. At the same time, the space distribution and the waveform inversion focal mechanisms of the earthquakes occurring at shallow depth (〈70 km) do not evidence Subduction Transform Edge Propagator (STEP) fault activity at the edges of the descending slab. In particular, no trace is found of dip-slip faulting along near vertical planes parallel to the slab edges, that is no seismic evidence is available of vertical motion between the subducting segment of the plate and the adjacent portion of it. Also, the seismicity distribution and mechanisms found at crustal depths in the study region do not match properly with the expected scenario of relative motion at the lateral borders of the overriding plate. Our earthquake locations and mechanisms together with GPS information taken from the literature highlight a residual, laterally very short subducting slab showing quasi-nil velocity of trench retreat and no present-day STEP activity, still capable however of causing strong normal-faulting earthquakes in the trench area through its gravity-induced shallow deformation in a weak-coupling scenario.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 42
    Publication Date: 2014-11-02
    Description: Rayleigh wave group velocity dispersion measurements from local and regional earthquakes are used to interpret the lithospheric structure in the Gulf of California region. We compute group velocity maps for Rayleigh waves from 10 to 150 s using earthquakes recorded by broad-band stations of the Network of Autonomously Recording Seismographs in Baja California and Mexico mainland, UNM in Mexico, BOR, DPP and GOR in southern California and TUC in Arizona. The study area is gridded in 120 longitude cells by 180 latitude cells, with an equal spacing of 10 10 km. Assuming that each gridpoint is laterally homogeneous, for each period the tomographic maps are inverted to produce a 3-D lithospheric shear wave velocity model for the region. Near the Gulf of California rift axis, we found three prominent low shear wave velocity regions, which are associated with mantle upwelling near the Cerro Prieto volcanic field, the Ballenas Transform Fault and the East Pacific Rise. Upwelling of the mantle at lithospheric and asthenospheric depths characterizes most of the Gulf. This more detailed finding is new when compared to previous surface wave studies in the region. A low-velocity zone in northcentral Baja at ~28ºN which extends east–south–eastwards is interpreted as an asthenospheric window. In addition, we also identify a well-defined high-velocity zone in the upper mantle beneath central-western Baja California, which correlates with the previously interpreted location of the stalled Guadalupe and Magdalena microplates. We interpret locations of the fossil slab and slab window in light of the distribution of unique post-subduction volcanic rocks in the Gulf of California and Baja California. We also observe a high-velocity anomaly at 50-km depth extending down to ~130 km near the southwestern Baja coastline and beneath Baja, which may represent another remnant of the Farallon slab.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 43
    Publication Date: 2014-11-02
    Description: We show that superresolution imaging in the far-field region of the sources and receivers is theoretically and practically possible if migration of resonant multiples is employed. A resonant multiple is one that bounces back and forth between two scattering points; it can also be the multiple between two smoothly varying interfaces as long as the reflection wave paths partially overlap and reflect from the same Fresnel zone. For a source with frequency f , compared to a one-way trip, N round trips in propagating between two scatterers increase the effective frequency by 2 N   f and decrease the effective wavelength by /(2 N ). Thus, multiples can, in principle, be used as high-frequency probes to estimate detailed properties of layers. Tests with both synthetic and field data validate this claim. Improved resolution by multiple imaging is not only feasible for crustal reflections, but might be applicable to mantle and core reverberations recorded by earthquake seismologists.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 44
    Publication Date: 2014-09-20
    Description: We develop a frequency-based approach to earthquake slip inversion that requires no prior information on the rupture velocity or slip-rate functions. Because the inversion is linear and is performed separately at each frequency, it is computationally efficient and suited to imaging the finest resolvable spatial details of rupture. We demonstrate the approach on synthetic seismograms based on the Source Inversion Validation Exercise 1 (SIV1) of a crustal M w 6.6 strike-slip earthquake recorded locally. A robust inversion approach is obtained by applying a combination of damping, smoothing and forcing zero slip at the edge of the fault model. This approach achieves reasonable data fits, overall agreement to the SIV1 model, including slip-rate functions of each subfault, from which its total slip, slip time history and rupture velocity can be extracted. We demonstrate the method's robustness by exploring the effects of noise, random timing errors, and fault geometry errors. The worst effects on the inversion are seen from errors in the assumed fault geometry.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 45
    Publication Date: 2014-09-20
    Description: Passive seismic methods using earthquakes can be applied for extracting body waves and obtaining information of subsurface structure. In this study, we retrieve direct and reflected plane waves by applying seismic interferometry to the recorded ground motion from a cluster of regional earthquakes. We apply upgoing/downgoing P/S wavefield decomposition, time windowing, and multidimensional deconvolution to improve the quality of the extraction of reflected waves with seismic interferometry. The wavefield separation and seismic interferometry based on multidimensional deconvolution allow us to reconstruct PP, PS, SP and SS reflected waves without unwanted crosstalk between P and S waves. From earthquake data, we obtain PP, PS and SS reflected plane waves that reflect off the same reflector, and estimate P - and S -wave velocities.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 46
    Publication Date: 2014-09-20
    Description: The representation of viscoelastic media in the time domain becomes more challenging with greater bandwidth of the propagating waves and number of travelled wavelengths. With the continuously increasing computational power, more extreme parameter regimes become accessible, which requires the reassessment and improvement of the standard ‘memory variable’ methods to implement attenuation in time-domain seismic wave-propagation methods. In this paper, we propose a method to minimize the error in the wavefield for a fixed complexity of the anelastic medium. This method consists of defining an appropriate misfit criterion based on a first-order analysis of how errors in the discretized medium propagate into errors in the wavefield and a simulated annealing optimization scheme to find the globally optimal parametrization. Furthermore, we derive an analytical time-stepping scheme for the memory variables that encode the strain history of the medium. Then we develop the coarse grained memory variable approach for the spectral element method (SEM) and benchmark it using the 2.5-D code AxiSEM for global body waves up to 1 Hz. Showing very good agreement with a reference solution, it also leads to a speedup of a factor of 5 in the anelastic part of the code (factor 2 in total) in this 2.5-D approach. A factor of 15 (3 in total) can be expected for the 3-D case compared to conventional implementations.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 47
    Publication Date: 2014-08-24
    Description: In the western Pacific, high-frequency seismic energy is carried to very great distances from the source. The Po and So phases with observed seismic velocities characteristic of the mantle lithosphere have complex and elongated waveforms that are well explained by a model of stochastic heterogeneity. However, in the eastern part of the Pacific Basin equivalent paths show muted Po and weak, or missing, So . Once established, it is hard to eliminate such guided Po and So energy in the mantle lithosphere by purely structural effects. Even sharp changes in lithospheric thickness or complex transitions at fracture zones only weaken the mantle ducted wave trains, but Po and So remain distinct. In contrast, the effect of attenuation is much more severe and can lead to suppression of the So phase to below the noise level after passage of a few hundred kilometres. The differing characteristics of Po and So across the Pacific can therefore be related directly to the thermal state via the enhanced attenuation in hotter regions, such as the spreading ridges and backarc regions.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 48
    Publication Date: 2014-10-01
    Description: The radially anisotropic shear velocity structure of the Earth's mantle provides a critical window on the interior dynamics of the planet, with isotropic variations that are interpreted in terms of thermal and compositional heterogeneity and anisotropy in terms of flow. While significant progress has been made in the more than 30 yr since the advent of global seismic tomography, many open questions remain regarding the dual roles of temperature and composition in shaping mantle convection, as well as interactions between different dominant scales of convective phenomena. We believe that advanced seismic imaging techniques, such as waveform inversion using accurate numerical simulations of the seismic wavefield, represent a clear path forwards towards addressing these open questions through application to whole-mantle imaging. To this end, we employ a ‘hybrid’ waveform-inversion approach, which combines the accuracy and generality of the spectral finite element method (SEM) for forward modelling of the global wavefield, with non-linear asymptotic coupling theory for efficient inverse modelling. The resulting whole-mantle model (SEMUCB-WM1) builds on the earlier successful application of these techniques for global modelling at upper mantle and transition-zone depths (≤800 km) which delivered the models SEMum and SEMum2. Indeed, SEMUCB-WM1 is the first whole-mantle model derived from fully numerical SEM-based forward modelling. Here, we detail the technical aspects of the development of our whole-mantle model, as well as provide a broad discussion of isotropic and radially anisotropic model structure. We also include an extensive discussion of model uncertainties, specifically focused on assessing our results at transition-zone and lower-mantle depths.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 49
    Publication Date: 2014-09-25
    Description: Anchor Bay and surrounding regions are located on the northwest coast of the island of Malta, Central Mediterranean. The area is characterized by a coastal cliff environment having an outcropping layer of hard coralline limestone (UCL) resting on a thick (up to 50 m) layer of clays and marls (Blue Clay, BC). This configuration gives rise to coastal instability effects, in particular lateral spreading phenomena and rock falls. Previous and ongoing studies have identified both lateral spreading rates and vertical motions of several millimetres per year. The area is an interesting natural laboratory as coastal detachment processes in a number of different stages can be identified and are easily accessible. We investigate the site dynamic characteristics of this study area by recording ambient noise time-series at more than 30 points, over an area of 0.07 km 2 , using a portable three-component seismograph. The time-series are processed to give both horizontal-to-vertical spectral ratio graphs (H/V) as well as frequency-dependent polarisation analysis. The H/V graphs illustrate and quantify aspects of site resonance effects due both to underlying geology as well as to mechanical resonance of partly or wholly detached blocks. The polarization diagrams indicate the degree of linearity and predominant directions of vibrational effects. H/V curves closer to the cliff edge show complex responses at higher frequencies, characteristic of the dynamic behaviour of individual detached blocks. Particle motion associated with the higher frequencies shows strongly directional polarization and a high degree of linearity at well-defined frequencies, indicative of normal-mode vibration. The stable plateau areas, on the other hand, show simple, single-peak H/V curves representative of the underlying stratification and no predominant polarization direction. These results, which will be compared with those from other experiments in the area, have important implications for the understanding of ongoing processes in geologically active and unstable coastal environments.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 50
    Publication Date: 2014-09-07
    Description: We focus on the relation between seismic and total postseismic afterslip following the Maule M w 8.8 earthquake on 2010 February 27 in central Chile. First, we calculate the cumulative slip released by aftershock seismicity. We do this by summing up the aftershock regions and slip estimated from scaling relations. Comparing the cumulative seismic slip with afterslip models we show that seismic slip of individual aftershocks exceeds locally the inverted afterslip model from geodetic constraints. As the afterslip model implicitly contains the displacements from the aftershocks, this reflects the tendency of afterslip models to smear out the actual slip pattern. However, it also suggests that locally slip for a number of the larger aftershocks exceeds the aseismic slip in spite of the fact that the total equivalent moment of the afterslip exceeds the cumulative moment of aftershocks by a large factor. This effect, seen weakly for the Maule 2010 and also for the Tohoku 2011 earthquake, can be explained by taking into account the uncertainties of the seismicity and afterslip models. In spite of uncertainties, the hypocentral region of the Nias 2005 earthquake is suggested to release a large fraction of moment almost purely seismically. Therefore, these aftershocks are not driven solely by the afterslip but instead their slip areas have probably been stressed by interseismic loading and the mainshock rupture. In a second step, we divide the megathrust of the Maule 2010 rupture into discrete cells and count the number of aftershocks that occur within 50 km of the centre of each cell as a function of time. We then compare this number to a time-dependent afterslip model by defining the ‘afterslip to aftershock ratio’ (ASAR) for each cell as the slope of the best fitting line when the afterslip at time t is plotted against aftershock count. Although we find a linear relation between afterslip and aftershocks for most cells, there is significant variability in ASAR in both the downdip and along-strike directions of the megathrust. We compare the spatial distribution of ASAR with the spatial distribution of seismic coupling, coseismic slip and Bouguer gravity anomaly, and in each case we find no significant correlation.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 51
    Publication Date: 2014-09-07
    Description: We analysed the conversion problem between teleseismic magnitudes ( M s and m b ) provided by the Seismological Bulletin of the International Seismological Centre and moment magnitudes ( M w ) provided by online moment tensor (MT) catalogues using the chi-square general orthogonal regression method (CSQ) that, differently from the ordinary least-square regression method (OLS), accounts for the measurement errors of both the predictor and response variables. To account for the non-linearity of the relationships, we used two types of curvilinear models: (i) the exponential model (EXP), recently proposed by the authors of the Global Catalogue sponsored by the Global Earthquake Model (GEM) Foundation and (ii) a connected bilinear (CBL) model, similar to that proposed by Ekström & Dziewonski, where two different linear trends at low and high magnitudes are connected by an arc of circle that preserves the continuity of the function and of its first derivative at the connecting points. For M s , we found that the regression curves computed for a global data set (GBL) are likely to be biased by the incompleteness of global MT catalogues for M w 〈5.0–5.5. In fact, the GBL curves deviate significantly from a similar regression curve computed for a Euro-Mediterranean data set (MED) integrated with the data provided by two regional MT catalogues including many more events with M w 〈 5.0–5.5. The GLB regression curves overestimate the M w proxies computed from M s up to 0.5 magnitude units. Hence for computing M w proxies at the global scale of M s ≤ 5.5, we suggest to adopt the coefficients obtained from the MED regression. The analysis of the frequency–magnitude relationship of the resulting M w proxy catalogues confirms the validity of this choice as the behaviour of b­ -value as a function of cut-off magnitude of the GBL data set is much more stable using such approach. The incompleteness of M w 's provided from MT global catalogues also affects the m b GBL data set but in this case the use of the CSQ regression method, in place of the OLS, mitigates the bias and then, at low magnitudes, the EXP regression curve computed from the more complete MED data set almost coincides with that computed from the GBL data set. Our results also indicate that the slope at low magnitudes of the M w – M s relationship is substantially consistent with the hypothesized theoretical value of 2/3 for M s 〈 5.0 while the slope of the M w – m b relationship at high magnitudes probably reaches the theoretically expected value of 2 only in the proximity of the upper limit of m b determinations in our data set ( m b  = 7.2).
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 52
    Publication Date: 2014-09-07
    Description: In this study, we present a new method for simulating the 3-D dynamic rupture process occurring on a non-planar fault. The method is based on the curved-grid finite-difference method (CG-FDM) proposed by Zhang & Chen and Zhang et al. to simulate the propagation of seismic waves in media with arbitrary irregular surface topography. While keeping the advantages of conventional FDM, that is computational efficiency and easy implementation, the CG-FDM also is flexible in modelling the complex fault model by using general curvilinear grids, and thus is able to model the rupture dynamics of a fault with complex geometry, such as oblique dipping fault, non-planar fault, fault with step-over, fault branching, even if irregular topography exists. The accuracy and robustness of this new method have been validated by comparing with the previous results of Day et al. , and benchmarks for rupture dynamics simulations. Finally, two simulations of rupture dynamics with complex fault geometry, that is a non-planar fault and a fault rupturing a free surface with topography, are presented. A very interesting phenomenon was observed that topography can weaken the tendency for supershear transition to occur when rupture breaks out at a free surface. Undoubtedly, this new method provides an effective, at least an alternative, tool to simulate the rupture dynamics of a complex non-planar fault, and can be applied to model the rupture dynamics of a real earthquake with complex geometry.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 53
    Publication Date: 2014-09-11
    Description: We present a numerical method to compute 3-D elastic waves in fully anisotropic axisymmetric media. This method is based on a decomposition of the wave equation into a series of uncoupled 2-D equations for which the dependence of the wavefield on the azimuth can be solved analytically. Four independent equations up to quadrupole order appear as solutions for moment-tensor sources located on the symmetry axis while single forces can be accommodated by two separate solutions up to dipole order. This decomposition gives rise to an efficient solution of the 3-D wave equation in a 2-D axisymmetric medium. First, we prove the validity of the decomposition of the wavefield in the presence of general anisotropy. Then we use it to derive the reduced 2-D equations of motions and discretize them using the spectral element method. Finally, we benchmark the numerical implementation for global wave propagation at 1 Hz and consider inner core anisotropy as an application for high-frequency wave propagation in anisotropic media at frequencies up to 2 Hz.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 54
    Publication Date: 2014-09-11
    Description: We have developed a wavelet-based double-difference (DD) seismic tomography method. Instead of solving for the velocity model itself, the new method inverts for its wavelet coefficients in the wavelet domain. This method takes advantage of the multiscale property of the wavelet representation and solves the model at different scales. A sparsity constraint is applied to the inversion system to make the set of wavelet coefficients of the velocity model sparse. This considers the fact that the background velocity variation is generally smooth and the inversion proceeds in a multiscale way with larger scale features resolved first and finer scale features resolved later, which naturally leads to the sparsity of the wavelet coefficients of the model. The method is both data- and model-adaptive because wavelet coefficients are non-zero in the regions where the model changes abruptly when they are well sampled by ray paths and the model is resolved from coarser to finer scales. An iteratively reweighted least squares procedure is adopted to solve the inversion system with the sparsity regularization. A synthetic test for an idealized fault zone model shows that the new method can better resolve the discontinuous boundaries of the fault zone and the velocity values are also better recovered compared to the original DD tomography method that uses the first-order Tikhonov regularization.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 55
    Publication Date: 2014-09-11
    Description: We show that it is possible to capture the oscillatory ground motion induced by the Tohoku-Oki event for periods ranging from 3 to 100 s using precise point positioning. We find that the ground motions of the sedimentary basins of Japan were large (respectively 〉0.15 m s –1 and 〉0.15 m s –2 for velocity and acceleration) even for periods larger than 3 s. We compare geodetic observables with a ground motion prediction equation designed for Japan seismicity and find that the spectral acceleration is well estimated for periods larger than 3 s and distances ranging from 100 to 500 km. At last, through the analysis of the displacement attenuation plots, we show that the 2011 Tohoku-Oki event is likely composed of multiple rupture patches as suggested before by time-reversal inversions of seismic data.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 56
    Publication Date: 2014-09-12
    Description: A geotechnical and geophysical campaign was performed at sites located in the alluvial plain of the river of Beirut (Lebanon), which is characterized by a significant lateral and vertical geological variability, along with anthropogenic disturbances in the first metres. The method combination has allowed detecting a shallow conductive low velocity layer of varying depth and thickness, corresponding to a soft clay layer embedded in coarser formations. This layer was found to exert strong control on the experimental dispersion curves (estimated from both active and passive experiments) characterized by a continuous mode superposition at high frequency, associated with an increase in phase velocity. Vs profiles in boreholes turned out to be of prime importance for adequately defining the parametrization before inversion and for ensuring the reliability of the inversion dispersive estimates at low frequency. A major output of this study is also to show that this low velocity layer, along with the strong shear velocity contrast at its bottom, significantly contributes to the site seismic response, and could make it difficult to use the measured H / V peak frequency as a proxy for the soil thickness over bedrock.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 57
    Publication Date: 2014-09-12
    Description: We present an analysis of the M w = 5.3 earthquake that occurred in the Southeast Indian Ridge on 2010 February 11 using USArray data. The epicentre of this event is antipodal to the USArray, providing us with an opportunity to observe in details the antipodal focusing of seismic waves in space and time. We compare the observed signals with synthetic seismograms computed for a spherically symmetric earth model (PREM). A beamforming analysis is performed over the different seismic phases detected at antipodal distances. Direct spatial snapshots of the signals and the beamforming results show that the focusing is well predicted for the first P -wave phases such as PKP or PP . However, converted phases ( SKSP , PPS ) show a deviation of the energy focusing to the south, likely caused by the Earth's heterogeneity. Focusing of multiple S -wave phases strongly deteriorates and is barely observable.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 58
    Publication Date: 2014-09-12
    Description: Global seismic tomography suffers from uncertainties in earthquake parameters routinely published in seismic catalogues. In particular, errors in earthquake location and origin-time may lead to strong biases in measured body wave delay-times and significantly pollute tomographic models. Common ways of dealing with this issue are to incorporate source parameters as additional unknowns into the linear tomographic equations, or to seek combinations of data to minimize the influence of source mislocations. We propose an alternative, physically-based method to desensitize direct S -wave delay-times to errors in earthquake location and origin-time. Our approach takes advantage of the fact that mislocation delay-time biases depend to first order on the earthquake-receiver azimuth, and to second order on the epicentral distance. Therefore, for every earthquake, we compute S -wave differential delay-times between optimized receiver pairs, such that a large part of their mislocation delay-time biases cancels out (for example origin-time fully subtracts out), while the difference of their sensitivity kernels remains sensitive to the model parameters of interest. Considering realistic, randomly distributed source mislocation vectors, as well as various levels of data noise and different synthetic Earths, we demonstrate that mislocation-related model errors are highly reduced when inverting for such differential delay-times, compared to absolute ones. The reduction is particularly rewarding for imaging the upper-mantle and transition zone. We conclude that using optimized receiver pairs is a suitable, low cost alternative to get rid of errors on earthquake location and origin-time for teleseismic direct S -wave traveltimes. Moreover, it can partly remove unilateral rupture propagation effects in cross-correlation delay-times, since they are similar to mislocation effects.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 59
    Publication Date: 2014-12-12
    Description: As the Earth's inhomogeneous and viscoelastic properties, seismic signal attenuation we are trying to mitigate is a long-standing problem facing with high-resolution techniques. For addressing such a problem in the fields of time–frequency transform, Gabor transform methods such as atom-window method (AWM) and molecular window method (MWM) have been reported recently. However, we observed that these methods might be much better if we partition the non-stationary seismic data into adaptive stationary segments based on the amplitude and frequency information of the seismic signal. In this study, we present a new method called amplitude-frequency partition (AFP) to implement this process in the time–frequency domain. Cases of a synthetic and field seismic data indicated that the AFP method could partition the non-stationary seismic data into stationary segments approximately, and significantly, a high-resolution result would be achieved by combining the AFP method with conventional spectral-whitening method, which could be considered superior to previous resolution-enhancement methods like time-variant spectral whitening method, the AWM and the MWM as well. This AFP method presented in this study would be an effective resolution-enhancement tool for the non-stationary seismic data in the fields of an adaptive time–frequency transform.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 60
    Publication Date: 2014-12-12
    Description: Full waveform inversion (FWI) of 3-D data sets has recently been possible thanks to the development of high performance computing. However, FWI remains a computationally intensive task when high frequencies are injected in the inversion or more complex wave physics (viscoelastic) is accounted for. The highest computational cost results from the numerical solution of the wave equation for each seismic source. To reduce the computational burden, one well-known technique is to employ a random linear combination of the sources, rather that using each source independently. This technique, known as source encoding, has shown to successfully reduce the computational cost when applied to real data. Up to now, the inversion is normally carried out using gradient descent algorithms. With the idea of achieving a fast and robust frequency-domain FWI, we assess the performance of the random source encoding method when it is interfaced with second-order optimization methods (quasi-Newton l -BFGS, truncated Newton). Because of the additional seismic modelings required to compute the Newton descent direction, it is not clear beforehand if truncated Newton methods can indeed further reduce the computational cost compared to gradient algorithms. We design precise stopping criteria of iterations to fairly assess the computational cost and the speed-up provided by the source encoding method for each optimization method. We perform experiment on synthetic and real data sets. In both cases, we confirm that combining source encoding with second-order optimization methods reduces the computational cost compared to the case where source encoding is interfaced with gradient descent algorithms. For the synthetic data set, inspired from the geology of Gulf of Mexico, we show that the quasi-Newton l -BFGS algorithm requires the lowest computational cost. For the real data set application on the Valhall data, we show that the truncated Newton methods provide the most robust direction of descent.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 61
    Publication Date: 2014-12-13
    Description: We use the Rayleigh integral (RI) as an approximation to the Helmholtz–Kirchoff integral to model infrasound generation and propagation from underground chemical explosions at distances of 250 m out to 5 km as part of the Source Physics Experiment (SPE). Using a sparse network of surface accelerometers installed above ground zero, we are able to accurately create synthetic acoustic waveforms and compare them to the observed data. Although the underground explosive sources were designed to be symmetric, the resulting seismic wave at the surface shows an asymmetric propagation pattern that is stronger to the northeast of the borehole. This asymmetric bias may be attributed to the subsurface geology and faulting of the area and is observed in the acoustic waveforms. We compare observed and modelled results from two of the underground SPE tests with a sensitivity study to evaluate the asymmetry observed in the data. This work shows that it is possible to model infrasound signals from underground explosive sources using the RI and that asymmetries observed in the data can be modelled with this technique.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 62
    Publication Date: 2014-12-17
    Description: The Terre Adélie and George V Land (East Antarctica) represent key areas for understanding tectonic relationships between terranes forming the Neoarchean-Palaeoproterozoic Terre Adélie Craton (TAC) and the neighbouring lithospheric blocks, together with the nature of its boundary. This region that represents the eastern border of the TAC is limited on its eastern side by the Mertz shear zone (MSZ) separating more recent Palaeozoic units from the craton. The MSZ, that recorded dextral strike-slip movement at 1.7 and 1.5 Ga, is likely correlated with the Kalinjala or Coorong shear zone in South Australia, east of the Gawler Craton and may therefore represent a frozen lithospheric-scale structure. In order to investigate the lithospheric structure of the TAC and the MSZ, we deployed from 2009 October to 2011 October four temporary seismic stations, which sampled the various lithospheric units of the TAC and of the neighbouring Palaeozoic block, together with the MSZ. We used receiver function method to deduce Moho depths and seismic anisotropy technique to infer the upper mantle deformation. Results from receiver functions analysis reveal Moho at 40–44 km depth beneath the TAC, at 36 km under the MSZ and at 28 km beneath the eastern Palaeozoic domain. The MSZ therefore delimits two crustal blocks of different thicknesses with a vertical offset of the Moho of 12 km. Seismic anisotropy deduced from SKS splitting at stations on the TAC shows fast polarisation directions () trending E–W, that is, parallel to the continental margin, and delay times ( t ) ranging from 0.8 to 1.6 s. These results are similar to the splitting parameters observed at the permanent GEOSCOPE Dumont D'Urville station (DRV: 95°N, t 1.1 s) located in the Palaeoproterozoic domain of TAC. On the MSZ, the small number of good quality measurements limits the investigation of the deep signature of the shear zone. However, the station in the Palaeozoic domain shows trending N60°E, which is significantly different to the trending measurements from stations on the TAC, suggesting that the MSZ may also represent a major frontier between the Neoarchean-Palaeoproterozoic and Palaeozoic terranes.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 63
    Publication Date: 2014-12-17
    Description: The seismic investigation of the lowermost mantle is in many places hampered by the lack of suitable source–receiver combinations that sample the D '' region and have to meet the requirements of a suitable epicentral distance range. The low velocity regions beneath the central Pacific and Atlantic Oceans in particular have been sampled in fewer places than circum Pacific regions. In this study, we use data from two recent ocean bottom seismometer (OBS) deployments for the Plume-Lithosphere Undersea Mantle Experiment (PLUME) around Hawaii to increase the coverage of the lower mantle with reflected P waves. Through stacking of the data we achieve significant reduction in noise levels. The most favourable epicentral distances to detect D '' reflections are around 70–79°. Most of our source–receiver combinations have distances less than that, thereby limiting the number of candidate observed reflections. Nevertheless, using array methods, we are able to test approximately 70 events for arrivals with slowness values and arrival times that would be consistent with a top-side reflection off a hypothetical D '' structure (PdP wave). Modelling these data with a 1-D reflectivity method, we identify a few places of detectable PdP waves, for which the velocity contrast in P - and S -wave velocity across the D '' reflector have to be relatively large (around 3–5 per cent increase and decrease, respectively) compared to other regions (e.g. beneath the Caribbean or Eurasia where the contrast is closer to 1–2 per cent). For larger distance ranges, smaller velocity contrasts are sufficient to cause observable reflections. This study shows that, despite the possible dominance of microseisms on OBS records, it is possible to use relatively short-period waves, with dominant periods as short as 3–7 s. Our findings suggest that, with future such deployments, OBS deployments will help to extend D '' studies to previously unmapped regions.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 64
    Publication Date: 2014-12-21
    Description: In the context of elastic wave propagation, the non-periodic homogenization asymptotic method allows to find a smooth effective medium and equations that correspond to the wave propagation in a given complex elastic or acoustic medium down to a given minimum wavelength. By smoothing all discontinuities and fine scales of the original medium, the homogenization technique considerably reduces meshing difficulties as well as the numerical cost associated with the wave equation solver, while producing the same waveform as for the original medium (up to the wanted accuracy). We present here a variation of the original method, allowing to homogenize the difference, or residual, between an original medium and a reference medium. This makes it possible to, for example, homogenize some specific parts of a model or to leave unchanged a specific interface while homogenizing the rest of the model. We present two examples of applications, one implying a complex geological shallow structure and the other involving the combination of deterministic and stochastic elastic models.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 65
    Publication Date: 2014-12-21
    Description: Converted phase (CP) elastic seismic signals are comparable in amplitude to the primary signals recorded at large offsets and have the potential to be used in seismic imaging and velocity analysis. We present an approach for CP elastic wave equation velocity analysis that does not use source information and is applicable to surface-seismic, microseismic, teleseismic and vertical seismic profile (VSP) studies. Our approach is based on the cross-correlation between reflected or transmitted PP and CP PS (and/or SS and CP PS) waves propagated backward in time, and is formulated as an optimization problem with a differential semblance criterion objective function for the simultaneous update of both P - and S -wave velocity models. The merit of this approach is that it is fully data-driven, uses full waveform information, and requires only one elastic backward propagation to form an image rather than the two (one forward and one backward) propagations needed for standard reverse-time migration. Moreover, as the method does not require forward propagation, it does not suffer from migration operator source aliasing when a small number of shots are used. We present a derivation of the method and test it with a synthetic model and field micro-seismic data.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 66
    Publication Date: 2014-12-25
    Description: We examine P -wave velocity structure at the base of the mantle beneath the western Pacific, near the western edge of the Pacific Large-Low Shear Velocity Province (LLSVP), using high-quality seismograms provided by a large-scale mobile broad-band seismic observation in northeastern China (the NECESSArray project). Forward modelling using the reflectivity method is conducted to explain the variation of P -wave traveltimes as a function of epicentral distance near the core shadow zone. Additionally, PcP–P traveltimes are examined to enlarge the survey area. As a result, a rapid variation of P -wave velocity is detected at the base of the mantle. Regions of thin (20–50 km thick) and low velocity (–2 to –5 per cent) layers at the base of the mantle are intersected by an 80-km-thick region with a high velocity (+2 per cent). A slightly fast region exists at the northwest of the region with the thin low-velocity layer. These layers are typically separated by several hundred kilometres and would be difficult to explain by thermal effects alone. These observations suggest that very complicated thermochemical reactions occur near the edge of the Pacific LLSVP.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 67
    Publication Date: 2014-10-17
    Description: We successfully apply the semi-global inverse method of simulated annealing to determine the best-fitting 1-D anisotropy model for use in acoustic frequency domain waveform tomography. Our forward problem is based on a numerical solution of the frequency domain acoustic wave equation, and we minimize wavefield phase residuals through random perturbations to a 1-D vertically varying anisotropy profile. Both real and synthetic examples are presented in order to demonstrate and validate the approach. For the real data example, we processed and inverted a cross-borehole data set acquired by Vale Technology Development (Canada) Ltd. in the Eastern Deeps deposit, located in Voisey's Bay, Labrador, Canada. The inversion workflow comprises the full suite of acquisition, data processing, starting model building through traveltime tomography, simulated annealing and finally waveform tomography. Waveform tomography is a high resolution method that requires an accurate starting model. A cycle-skipping issue observed in our initial starting model was hypothesized to be due to an erroneous anisotropy model from traveltime tomography. This motivated the use of simulated annealing as a semi-global method for anisotropy estimation. We initially tested the simulated annealing approach on a synthetic data set based on the Voisey's Bay environment; these tests were successful and led to the application of the simulated annealing approach to the real data set. Similar behaviour was observed in the anisotropy models obtained through traveltime tomography in both the real and synthetic data sets, where simulated annealing produced an anisotropy model which solved the cycle-skipping issue. In the real data example, simulated annealing led to a final model that compares well with the velocities independently estimated from borehole logs. By comparing the calculated ray paths and wave paths, we attributed the failure of anisotropic traveltime tomography to the breakdown of the ray-theoretical approximation in the vicinity of strong velocity discontinuities.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 68
    Publication Date: 2014-10-16
    Description: Seismic traveltimes and their spatial derivatives are the basis of many imaging methods such as pre-stack depth migration and tomography. A common approach to compute these quantities is to solve the eikonal equation with a finite-difference scheme. If many recently published algorithms for resolving the eikonal equation do now yield fairly accurate traveltimes for most applications, the spatial derivatives of traveltimes remain very approximate. To address this accuracy issue, we develop a new hybrid eikonal solver that combines a spherical approximation when close to the source and a plane wave approximation when far away. This algorithm reproduces properly the spherical behaviour of wave fronts in the vicinity of the source. We implement a combination of 16 local operators that enables us to handle velocity models with sharp vertical and horizontal velocity contrasts. We associate to these local operators a global fast sweeping method to take into account all possible directions of wave propagation. Our formulation allows us to introduce a variable grid spacing in all three directions of space. We demonstrate the efficiency of this algorithm in terms of computational time and the gain in accuracy of the computed traveltimes and their derivatives on several numerical examples.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 69
    Publication Date: 2014-10-17
    Description: Our study compares the seismic properties between the flat and normal subduction regions in central Chile, to better understand the links between the slab geometry, surface deformation and the deeper structures. In comparison with previous studies, we show the most complete 3-D regional seismic tomography images for this region, in which we use (1) a larger seismic data set compiled from several short-term seismic catalogues, (2) a denser seismic array allowing a better resolution of the subduction zone from the trench to the backarc and into the upper ~30 km of the slab and (3) a starting 1-D background velocity model specifically calculated for this region and refined over the years. We assess and discuss our tomography results using regional seismic attenuation models and estimating rock types on the basis of pressure and temperature conditions computed from thermomechanical models. Our results show significant seismic differences between the flat and normal subduction zones. As expected, the faster seismic velocities and increased seismicity within the flat slab and overriding lithosphere are generally consistent with a cooler thermal state. Our results are also consistent with dehydration of the mantle above the subducted Juan Fernandez Ridge at the eastern tip of the flat slab segment, indicating that the latter retains some fluids during subduction. However, fluids in the upper portion of the flat slab segment are not seismically detected, since we report instead fast slab seismic velocities which contradict the argument of its buoyancy being the cause of horizontal subduction. The forearc region, above the flat slab, exhibits high Vs and very low Vp / Vs ratios, uncorrelated with typical rock compositions, increased density or reduced temperature; this feature is possibly linked with the aftershock effects of the M w7.1 1997 Punitaqui earthquake, the flat slab geometry and/or seismic anisotropy. At the surface, the seismic variations correlate with the geological terranes. The Andean crust is strongly reduced in seismic velocities along the La Ramada–Aconcagua deformation belt, suggesting structural damage. Slow seismic velocities along the Andean Moho match non-eclogitized hydrated rocks, consistent with a previous delamination event or a felsic composition, which in turn supports the extent of the Chilenia terrane at these depths. We confirm previous studies that suggest that the Cuyania terrane in the backarc region is mafic and contains an eclogitized lower crust below 50-km depth. We also hypothesize major Andean basement detachment faults (or shear zones) to extend towards the plate interface and canalize slab-derived fluids into the continental crust.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 70
    Publication Date: 2014-10-17
    Description: The most common type of waves used for probing anisotropy of rocks in laboratory is the direct P wave. Information potential of the measured P -wave velocity, however, is limited. In rocks displaying weak triclinic anisotropy, the P -wave velocity depends just on 15 linear combinations of 21 elastic parameters, called the weak-anisotropy parameters. In strong triclinic anisotropy, the P -wave velocity depends on the whole set of 21 elastic parameters, but inversion for six of them is ill-conditioned and these parameters are retrieved with a low accuracy. Therefore, in order to retrieve the complete elastic tensor accurately, velocities of S waves must also be measured and inverted. For this purpose, we developed a lab facility which allows the P - and S -wave ultrasonic sounding of spherical rock samples in 132 directions distributed regularly over the sphere. The velocities are measured using a pair of P -wave sensors with the transmitter and receiver polarized along the radial direction and using two pairs of S -wave sensors with the transmitter and receiver polarized tangentially to the spherical sample in mutually perpendicular directions. We present inversion methods of phase and ray velocities for elastic parameters describing general triclinic anisotropy. We demonstrate on synthetic tests that the inversion becomes more robust and stable if the S -wave velocities are included. This applies even to the case when the velocity of the S waves is measured in a limited number of directions and with a significantly lower accuracy than that of the P wave. Finally, we analyse velocities measured on a rock sample from the Outokumpu deep drill hole, Finland. We present complete sets of elastic parameters of the sample including the error analysis for several levels of confining pressure ranging from 0.1 to 70 MPa.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 71
    Publication Date: 2014-10-19
    Description: We use normal-mode splitting functions in addition to surface wave phase anomalies, body wave traveltimes and long-period waveforms to construct a 3-D model of anisotropic shear wave velocity in the Earth's mantle. Our modelling approach inverts for mantle velocity and anisotropy as well as transition-zone discontinuity topographies, and incorporates new crustal corrections for the splitting functions that are consistent with the non-linear corrections we employ for the waveforms. Our preferred anisotropic model, S362ANI+M, is an update to the earlier model S362ANI, which did not include normal-mode splitting functions in its derivation. The new model has stronger isotropic velocity anomalies in the transition zone and slightly smaller anomalies in the lowermost mantle, as compared with S362ANI. The differences in the mid- to lowermost mantle are primarily restricted to features in the Southern Hemisphere. We compare the isotropic part of S362ANI+M with other recent global tomographic models and show that the level of agreement is higher now than in the earlier generation of models, especially in the transition zone and the lower mantle. The anisotropic part of S362ANI+M is restricted to the upper 300 km in the mantle and is similar to S362ANI. When radial anisotropy is allowed throughout the mantle, large-scale anisotropic patterns are observed in the lowermost mantle with v SV  〉  v SH beneath Africa and South Pacific and v SH  〉  v SV beneath several circum-Pacific regions. The transition zone exhibits localized anisotropic anomalies of ~3 per cent v SH  〉  v SV beneath North America and the Northwest Pacific and ~2 per cent v SV  〉  v SH beneath South America. However, small improvements in fits to the data on adding anisotropy at depth leave the question open on whether large-scale radial anisotropy is required in the transition zone and in the lower mantle. We demonstrate the potential of mode-splitting data in reducing the trade-offs between isotropic velocity and anisotropy in the lowermost mantle for the even-degree variations. Spurious anisotropic variations in the mid-mantle are also suppressed with the addition of mode-splitting data.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 72
    Publication Date: 2014-09-27
    Description: We describe a methodology for quantitatively characterizing the fractured nature of a hydrocarbon or geothermal reservoir from surface seismic data under a Bayesian inference framework. The method combines different kinds of measurements of fracture properties to find a best-fitting model while providing estimates of the uncertainty of model parameters. Fractures provide pathways for fluid flow in a reservoir, and hence, knowledge about a reservoir's fractured nature can be used to enhance production from the reservoir. The fracture properties of interest in this study (to be inferred) are fracture orientation and excess compliance, where each of these properties are assumed to vary spatially over a 2-D horizontal grid which is assumed to represent the top of a reservoir. The Bayesian framework in which the inference problem is cast has the key benefits of (1) utilization of a prior model that allows geological information to be incorporated, (2) providing a straightforward means of incorporating all measurements (across the 2-D spatial grid) into the estimates at each gridpoint, (3) allowing different types of measurements to be combined under a single inference procedure and (4) providing a measure of uncertainty in the estimates. The observed data are taken from a 2-D array of surface seismic receivers responding to an array of surface sources. Well understood features from the seismic traces are extracted and treated as the observed data, namely the P -wave reflection amplitude variation with acquisition azimuth and offset (amplitude versus azimuth data) and fracture transfer function (FTF) data. Amplitude versus azimuth data are known to be more sensitive to fracture properties when the fracture spacing is significantly smaller than the seismic wavelength, whereas FTF data are more sensitive to fracture properties when the fracture spacing is on the order of the seismic wavelength. Combining these two measurements has the benefit of allowing inferences to be made about fracture properties over a larger range of fracture spacing than otherwise attainable. Geophysical forward models for the measurements are used to arrive at likelihood models for the data. The prior distribution for the fracture variables is obtained by defining a Markov random field over the lateral 2-D grid where we wish to obtain fracture properties, where this method for defining the prior has the added benefit of allowing for non-stationarity in the resulting model covariance. The fracture variables are then inferred by application of loopy belief propagation to yield approximations for the posterior marginal distributions of the fracture properties, as well as the maximum a posteriori and Bayes least-squares (posterior mean) estimates of these properties. Verification of the inference procedure is performed using a synthetic data set, where the estimates obtained are shown to be at or near ground truth for the full range of fracture spacings for fracture orientation and at low fracture spacings for excess compliance estimates.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 73
    Publication Date: 2014-09-27
    Description: In this study, new intensity-distance attenuation law is presented, using directly the intensity observations, rather than the subjective, and sometimes controversial, isoseismal lines. This intensity-distance attenuation law is the only one defined for Portugal mainland, which is expressed as a function of magnitude. We computed this attenuation law using the slope and the intercept of the logarithmic regression of 25 events, with magnitudes between 4.4 and 6.2. Using the Bakun and Wentworth method (1997), this new attenuation law allows performing better results in the earthquake epicentral position and magnitude estimations of the 1909 Benavente event than the Atkinston and Boore attenuation law (1997). This law also gives good results in the study of site effects, presenting good matches between intensity residuals and geological structures where site effects are expected.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 74
    Publication Date: 2014-09-30
    Description: We infer 3-D localized shear velocity structure in the lowermost 400 km of the mantle at the western edge of the Pacific large low shear velocity province (LLSVP) by applying waveform inversion to transverse component body-wave waveforms from the F-net seismic array in Japan. Our data set consists of relatively long period (12.5–200 s) broad-band seismic waveforms of Tonga-Fiji deep focus and intermediate deep earthquakes. We conduct several tests to confirm the robustness of the inversion results. We find two low-velocity zones at the bottom of the target region, with a high-velocity zone in the middle, and a low-velocity zone above the high-velocity zone and contiguous with the two deeper low-velocity zones at a depth of 200–300 km above the core-mantle boundary (CMB). This supports the idea that the Pacific LLSVP may be an aggregation of small upwelling plumes rather than a single large thermochemical pile.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 75
    Publication Date: 2014-06-21
    Description: Samples of shales from the Ordovician Bongabinni and Goldwyer source rock formations were recovered from the Canning Basin (Western Australia). Attenuation was experimentally measured on preserved plugs from these formations in the frequency range between 10 –2 and 10 2 Hz. Samples cored with different orientations with respect to the sedimentary bedding were prepared and tested in their native saturated state and after drying in the oven at 105 °C for 24 hr to assess the effect of fluids and of the sediment anisotropy on attenuation. To aid the interpretation of the experimental results, the clay-rich samples were characterized in terms of mineralogy, water content, porosity, permeability and microstructure. The two shales have significantly different quality factors; and this is seen to be dependent on both the saturation state of the samples and the propagation direction of the oscillatory signal. The attenuation coefficient for compression/extension parallel to bedding is less than that vertical to bedding in both the preserved and partially dehydrated situations. No frequency dependency is observed in the preserved samples within the range of frequencies explored in this study. On the other hand partially saturated samples show peaks in attenuation at around 40 Hz when the stress perturbation is transmitted normal to the macroscopic bedding. The interpretation of the attenuation measurements in terms of well-established theoretical models is discussed in view of the physical characteristics and microstructure of the tested rocks.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 76
    Publication Date: 2014-06-21
    Description: We examine seismic attenuation in the northern South Island, New Zealand, where subduction transitions to oblique collision, and plate motion occurs along multiple crustal faults overlying the subducted slab. The 3-D inversions derive Q (1/attenuation) using path attenuation t * observations for 334 distributed earthquakes recorded on permanent and temporary stations, including both velocity and acceleration records. A 2.5 s window was used for P spectra, but for S spectra longer varied lengths were selected around the predicted S arrival, using the 5–95 per cent energy integral. The Q results highlight many aspects of the structure more clearly than previously derived seismic velocity models, including a high Q slab, low Q basins, moderately low Q active fault regions, and thick lithosphere. Qs tends to be greater than Qp , except in low Q shallow upper crust. The mantle above the slab does not exhibit low Q , unlike mantle to the north beneath the volcanic region of central North Island, and is inferred to be cool and stagnant with some vertical flux of slab dehydration fluid. In the brittle crust, low Q is imaged along those faults with most recent seismicity and may be related to distributed microfractures. In the ductile crust of the greywacke terranes, zones of low Q under the faults are attributed to localized ductile deformation with high strain-rate and grain size reduction, consistent with numerical models showing the development of enhanced strain-rate zones above the strong underlying slab. In contrast the Christchurch region has no ductile lower crust and instead has high Q indicative of strong mafic rocks at 12 km depth.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 77
    Publication Date: 2014-06-22
    Description: Numerical simulation of repeated occurrences of slip events on a fault patch (asperity) is used to interpret the mechanism of irregular sequences of slip events. The fault is uniformly shear loaded at a constant rate, and the frictional stress acting on the fault is assumed to obey a rate- and state-dependent friction (RSF) law. A circular patch with velocity-weakening frictional property is embedded in the fault, which apart from this has velocity-strengthening frictional property. The numerical simulations are conducted using various characteristic slip distances L of the RSF law. For small values of L seismic slip events (earthquakes) repeatedly occur at regular intervals. With increasing L , the recurrence of slip events becomes more complex. A period doubled slip pattern, where seismic and aseismic slip events alternately occur, multiperiodic patterns and aperiodic patterns occur. At the same time, slip tends to become aseismic with increasing L . The distributions of shear stress on the fault just before slip events are variable because of variation in the residual stress of the preceding slip event and the shear stress generated by aseismic sliding during interseismic periods. These variations in shear stress cause the complex sequence of slip events seen here. An iteration map of the recurrence intervals of slip events for an aperiodic sequence of slip events is expressed by a simple curve, indicating that the timing of an event is predictable from the previous time interval, and the sequence of slip events exhibits deterministic chaos. To help interpret these results for a sequence of slip events on a velocity-weakening patch embedded in a velocity-strengthening region, a numerical simulation is conducted of slip on a velocity-weakening patch enclosed by a permanently locked region. In this case, no complex recurrence of slip events is observed. When L is less than a critical value, seismic slip events repeatedly occur at a constant interval. Stable sliding occurs when L is larger than the critical value. This result indicates that the complex slip behaviour seen for a velocity-weakening patch embedded in a velocity-strengthening region is caused by the interaction between the velocity-weakening and velocity-strengthening regions.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 78
    Publication Date: 2014-07-13
    Description: We carry out a joint inversion of surface wave dispersion curves and teleseismic shear wave arrival times across the Tibetan collision zone, from just south of the Himalaya to the Qaidam Basin at the northeastern margin of the plateau, and from the surface to 600 km depth. The surface wave data consist of Rayleigh-wave group dispersion curves, mainly in the period range from 10 to 70 s, with a maximum of 2877 source–receiver pairs. The body wave data consist of more than 8000 S -wave arrival times recorded from 356 telesesmic events. The tomographic images show a ‘wedge’ of fast seismic velocities beneath central Tibet that starts underneath the Himalaya and reaches as far as the Bangong–Nujiang Suture (BNS). In our preferred interpretation, in central Tibet the Indian lithosphere underthrusts the plateau to approximately the BNS, and then subducts steeply. Further east, Indian lithosphere appears to be subducting at an angle of ~45°. We see fast seismic velocities under much of the plateau, as far as the BNS in central Tibet, and as far as the Xiangshuihe–Xiaojiang Fault in the east. At 150 km depth, the fast region is broken by an area ~300 km wide that stretches from the northern edge of central Tibet southeastwards as far as the Himalaya. We suggest that this gap, which has been observed previously by other investigators, represents the northernmost edge of the Indian lithosphere, and is a consequence of the steepening of the subduction zone from central to eastern Tibet. This also implies that the fast velocities in the northeast have a different origin, and are likely to be caused by lithospheric thickening or small-scale subduction of Asian lithosphere. Slow velocities observed to the south of the Qaidam suggest that the basin is not subducting. Finally, we interpret fast velocities below 400 km as subducted material from an earlier stage of the collision that has stalled in the transition zone. Its position to the south of the present subduction is likely to be due to the relative motion of India to the northeast.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 79
    Publication Date: 2014-07-13
    Description: Probabilistic seismic hazard models (PSHM) are used for quantifying the seismic hazard at a site or a grid of sites. In this study, a methodology is proposed to compare the distribution of the expected number of sites with exceedance with the observed number considering an acceleration threshold at a set of recording sites. The method is applied to France and Turkey. The French accelerometric database is checked to produce a reliable accelerometric data set. In addition, we also used a synthetic data set inferred from an instrumental catalogue combined with a ground-motion prediction equation. The results show that the MEDD2002 and AFPS2006 PSH models overestimate the number of sites with exceedance for low acceleration levels (below 40 cm s –2 ) or short return periods (smaller than 50 yr for AFPS2006 and 475 yr for MEDD2002). For larger acceleration levels, there are few observations and none of the models is rejected. In Turkey, the SHARE hazard estimates can be tested against ground-motion levels of interest in earthquake engineering. As the completeness issue is crucial, the recorded data at each station is analysed to detect potential gaps in the recording. As most accelerometric stations are located on soil, accelerations at rock are estimated using a site-amplification model. Different minimum intersite distances and station configurations are considered. The observed numbers of sites with exceedance are well within the bounds of the predicted distribution for accelerations between 103 and 397 cm s –2 . For higher levels, both the observed number and the predicted percentile 2.5 are zero, and no conclusion can be drawn.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 80
    Publication Date: 2014-07-13
    Description: This study presents a depth inversion of Scholte wave group and phase velocity maps obtained from cross-correlation of 6.5 hr of noise data from the Valhall Life of Field Seismic network. More than 2 600 000 vertical–vertical component cross-correlations are computed from the 2320 available sensors, turning each sensor into a virtual source emitting Scholte waves. We used a traditional straight-ray surface wave tomography to compute the group velocity map. The phase velocity maps have been computed using the Eikonal tomography method. The inversion of these maps in depth are done with the Neighbourhood Algorithm. To reduce the number of free parameters to invert, geological a priori information are used to propose a power-law 1-D velocity profile parametrization extended with a gaussian high-velocity layer where needed. These parametrizations allowed us to create a high-resolution 3-D S -wave model of the first 600 m of the Valhall subsurface and to precise the locations of geological structures at depth. These results would have important implication for shear wave statics and monitoring of seafloor subsidence due to oil extraction. The 3-D model could also be a good candidate for a starting model used in full-waveform inversions.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 81
    Publication Date: 2014-07-13
    Description: Cross-correlation and cross-spectral time delays often exhibit strong outliers due to ambiguities or cycle jumps in the correlation function. Their number increases when signal-to-noise, signal similarity or spectral bandwidth decreases. Such outliers heavily determine the time-delay probability density function and the results of further computations (e.g. double-difference location and tomography) using these time delays. In the present research we expressed cross-correlation as a function of the squared difference between signal amplitudes and show that they are closely related. We used this difference as a cost function whose minimum is reached when signals are aligned. Ambiguities may be removed in this function by using a priori information. We propose using the traveltime difference as a priori time-delay information. By modelling the probability density function of the traveltime difference by a Cauchy distribution and the probability density function of the data (differences of seismic signal amplitudes) by a Laplace distribution we were able to find explicitly the time-delay a posteriori probability density function. The location of the maximum of this a posteriori probability density function is the maximum a p osteriori time-delay estimation for earthquake signals. Using this estimation to calculate time delays for earthquakes on the south flank of Kilauea statistically improved the cross-correlation time-delay estimation for these data and resulted in successful double-difference relocation for an increased number of earthquakes. This robust time-delay estimation improves the spatiotemporal resolution of seismicity rates in the south flank of Kilauea.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 82
    Publication Date: 2014-07-19
    Description: Fracture shear-dilatancy is an essential process for enhancing the permeability of deep geothermal reservoirs, and is usually accompanied by the radiation of seismic waves. However, the hazard and risk perspective of induced seismicity research typically focuses only on the question of how to reduce the occurrence of induced earthquakes. Here we present a quantitative analysis of seismic hazard as a function of the two key factors defining an enhanced geothermal system: The permeability enhancement, and the size of the stimulated reservoir. Our model has two coupled components: (1) a pressure diffusion model and (2) a stochastic seismicity model. Permeability is increased in the source area of each induced earthquake depending on the amount of slip, which is determined by the magnitude. We show that the few largest earthquakes (i.e. 5–10 events with M ≥ 1.5) contribute more than half of the total reservoir stimulation. The results further indicate that planning and controlling of reservoir engineering operations may be compromised by the considerable variability of maximum observed magnitude, reservoir size, the Gutenberg–Richter b -value and Shapiro's seismogenic index (i.e. a measure of seismic reactivity of a reservoir) that arises from the intrinsic stochastic nature of induced seismicity. We also find that injection volume has a large impact on both reservoir size and seismic hazard. Injection rate and injection scheme have a negligible effect. The impact of site-specific parameters on seismicity and reservoir properties is greater than that of the injected volume. In particular, conditions that lead to high b -values—possibly a low differential stress level—have a high impact on seismic hazard, but also reduce the efficiency of the stimulation in terms of permeability enhancement. Under such conditions, target reservoir permeability can still be achieved without reaching an unacceptable level of seismic hazard, if either the initial reservoir permeability is high or if several fractures are stimulated. The proposed methodology is a first step towards including induced seismic hazard analysis into the design of reservoir stimulation in a quantitative and robust manner.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 83
    Publication Date: 2014-07-19
    Description: Three large earthquakes occurred in the Ashikule stepover zone, NW Tibet in 2008 ( M w 7.1), 2012 ( M w 6.2) and 2014 ( M w 6.9). In this paper we use InSAR data to examine the 2008 event in detail, and place it in the context of both recent/possible future events and regional tectonic environment. We present InSAR data covering the coseismic and post-seismic phases of the 2008 event, and invert for slip distributions during both phases in order to examine the spatial relationship between earthquake rupture and afterslip. To account for the curved rupture trace as mapped in the field, we model the slip on a non-planar fault. A change in slip sense from left-lateral in the north to extensional in the south is consistent with the focal mechanism of aftershocks. We find that afterslip occurs around the perimeter of the coseismic slip, although in a patchy way, as seen in other normal faulting case studies. We calculate the Coulomb stress changes imparted by the 2008 earthquake on neighbouring faults, including stress loading on the subsequent rupture zones of the 2012 and 2014 earthquakes. We also compute the combined loading effect of the 2008, 2012 and 2014 earthquakes on the nearby Altyn Tagh Fault, which hasn't experienced a major earthquake since early last century. This study demonstrates that stepover zone failure can increase stresses on bounding strike-slip faults, which likely has relevance in analogous tectonic environments elsewhere in the world.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 84
    Publication Date: 2014-07-03
    Description: Source–receiver interferometric imaging can be used to synthesize a subsurface acoustic or elastic image, consisting of a zero-time, zero-offset response (or Green's function) between a colocated pseudo-source and pseudo-receiver placed at each point in the subsurface image. However, if the imaging process does not properly account for multiple reflections, and enclosing boundaries of sources and receivers are not available, the image shows artefacts, poorly illuminated areas and distorted image amplitudes. Here we demonstrate with numerical examples that two-sided non-linear imaging provides the best elastic pure-mode ( PP and SS ) and converted-mode ( PS ) images, having higher resolution and more uniform illumination than those obtained from both one-sided linear imaging and from other intermediate steps of imaging (e.g. non-linear one-sided, linear two-sided). We also propose practical approaches to construct the additional fields required by two-sided non-linear imaging without the need for a detailed velocity model and receivers (and/or sources) in the subsurface. Moreover, when conversions are used for imaging, ‘true-amplitude’ images (here true-amplitude means properly retrieving amplitudes that represent the zero-time, zero-offset elastic response) should theoretically vanish because neither P -to- S or S -to- P conversions arise at zero-time and zero-offset. Applying a correction procedure that accounts for the polarity reversal in PS (or SP ) single-shot images helps with their structural interpretation but results in an unphysical estimate of the subsurface response and uninterpretable amplitudes. This suggests that there are advantages in exploiting pure-mode SS reflections/transmissions, in addition to converted waves only, because they require no polarity correction and the resulting image contains meaningful amplitudes that are proportional to the local shear-wave properties of the medium.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 85
    Publication Date: 2014-07-03
    Description: We present a time-independent gridded earthquake rate forecast for the European region including Turkey. The spatial component of our model is based on kernel density estimation techniques, which we applied to both past earthquake locations and fault moment release on mapped crustal faults and subduction zone interfaces with assigned slip rates. Our forecast relies on the assumption that the locations of past seismicity is a good guide to future seismicity, and that future large-magnitude events occur more likely in the vicinity of known faults. We show that the optimal weighted sum of the corresponding two spatial densities depends on the magnitude range considered. The kernel bandwidths and density weighting function are optimized using retrospective likelihood-based forecast experiments. We computed earthquake activity rates ( a - and b -value) of the truncated Gutenberg–Richter distribution separately for crustal and subduction seismicity based on a maximum likelihood approach that considers the spatial and temporal completeness history of the catalogue. The final annual rate of our forecast is purely driven by the maximum likelihood fit of activity rates to the catalogue data, whereas its spatial component incorporates contributions from both earthquake and fault moment-rate densities. Our model constitutes one branch of the earthquake source model logic tree of the 2013 European seismic hazard model released by the EU-FP7 project ‘Seismic HAzard haRmonization in Europe’ (SHARE) and contributes to the assessment of epistemic uncertainties in earthquake activity rates. We performed retrospective and pseudo-prospective likelihood consistency tests to underline the reliability of our model and SHARE's area source model (ASM) using the testing algorithms applied in the collaboratory for the study of earthquake predictability (CSEP). We comparatively tested our model's forecasting skill against the ASM and find a statistically significant better performance for testing periods of 10–20 yr. The testing results suggest that our model is a viable candidate model to serve for long-term forecasting on timescales of years to decades for the European region.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 86
    Publication Date: 2014-07-03
    Description: To estimate the slowness vector of infrasound waves propagating across an infrasound array, it is often considered that the sensors are located in a perfectly horizontal plane (2-D approximation). However, the arrays are not planar and differences between sensor altitudes cannot be neglected without introducing biases when estimating the parameters of interest (backazimuth and incidence). A closed-formula of this error depending on the geometry of the array and the wave incidence is presented. Since the unbiased 3-D estimation of the slowness parameters results in a significant alteration of the variance, a metric based on the mean square error is proposed. We found it useful to compare the 3-D to the 2-D processed results. We show the 3-D estimator does not always give the best estimates. We propose also a formulation of the boundary that allow us to choose between these two estimators depending on the situation (arrays, incidence and signal-to-noise ratios). Finally, we compare these two approaches (2-D/3-D) to all International Monitoring System arrays with synthetic data, and perform a comparative estimation of backazimuth for real data.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 87
    Publication Date: 2014-07-03
    Description: Microseismic monitoring is an essential tool for the characterization of hydraulic fractures. Fast estimation of the parameters that define a microseismic event is relevant to understand and control fracture development. The amount of data contained in the microseismic records however, poses a challenge for fast continuous detection and evaluation of the microseismic source parameters. Work inspired by the emerging field of Compressive Sensing has showed that it is possible to evaluate source parameters in a compressed domain, thereby reducing processing time. This technique performs well in scenarios where the amplitudes of the signal are above the noise level, as is often the case in microseismic monitoring using downhole tools. This paper extends the idea of the compressed domain processing to scenarios of microseismic monitoring using surface arrays, where the signal amplitudes are commonly at the same level as, or below, the noise amplitudes. To achieve this, we resort to the use of an imaging operator, which has previously been found to produce better results in detection and location of microseismic events from surface arrays. The operator in our method is formed by full-waveform elastodynamic Green's functions that are band-limited by a source time function and represented in the frequency domain. Where full-waveform Green's functions are not available, ray tracing can also be used to compute the required Green's functions. Additionally, we introduce the concept of the compressed inverse, which derives directly from the compression of the migration operator using a random matrix. The described methodology reduces processing time at a cost of introducing distortions into the results. However, the amount of distortion can be managed by controlling the level of compression applied to the operator. Numerical experiments using synthetic and real data demonstrate the reductions in processing time that can be achieved and exemplify the process of selecting the compression rate that produces a tolerable amount of distortion into the results.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 88
    Publication Date: 2014-06-21
    Description: The topography of the core–mantle boundary (CMB) is directly linked to the dynamics of both the mantle and the outer core, although it is poorly constrained and understood. Recent studies have produced topography models with mutual agreement up to degree 2. A broad-band waveform inversion strategy is introduced and applied here, with relatively low computational cost and based on a first-order Born approximation. Its performance is validated using synthetic waveforms calculated in theoretical earth models that include different topography patterns with varying lateral wavelengths, from 600 to 2500 km, and magnitudes (~10 km peak-to-peak). The source–receiver geometry focuses mainly on the P diff , PKP , PcP and ScS phases. The results show that PKP branches, PcP and ScS generally perform well and in a similar fashion, while P diff yields unsatisfactory results. We investigate also how 3-D mantle correction influences the output models, and find that despite the disturbance introduced, the models recovered do not appear to be biased, provided that the 3-D model is correct. Using cross-correlated traveltimes, we derive new topography models from both P and S waves. The static corrections used to remove the mantle effect are likely to affect the inversion, compromising the agreement between models derived from P and S data. By modelling traveltime residuals starting from sensitivity kernels, we show how the simultaneous use of volumetric and boundary kernels can reduce the bias coming from mantle structures. The joint inversion approach should be the only reliable method to invert for CMB topography using absolute cross-correlation traveltimes.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 89
    Publication Date: 2014-06-21
    Description: We introduce the single-station cross-correlation (SC) technique of processing ambient seismic noise and compare its results with the established cross-correlation (CC) and autocorrelation (AC) techniques. While CC is the correlation of the signals of two seismic stations with each other and AC is the correlation of a signal with itself, SC is the correlation of two different components of a single three-component seismic sensor. The comparison of the three different correlation techniques shows that CCs give the best results at frequencies below 0.5 Hz and that SCs give the best results at higher frequencies. In all three processing techniques, ambient seismic noise is correlated in order to reconstruct the Green's function describing the wave propagation between the first and the second sensor. By relating the coda parts of the daily Green's functions with the long-term reference Green's functions, shear wave velocity changes are determined. Here, we apply this technique to the data of 20 seismic stations in the surroundings of the fault zone of the Iwate-Miyagi Nairiku earthquake ( M W  = 6.9), which occurred on 2008 June 13, UTC (2008 June 14, Japan Standard Time) in the northern part of the Japanese island Honshu. The data range from 2008 January to 2011 June and therefore include the Tohoku earthquake ( M W  = 9.0), which occurred on 2011 March 11, off the coast of northern Honshu. The data are analysed in five different frequency ranges between 0.125 and 4.0 Hz. The data show coseismic velocity changes for both earthquakes followed by a post-seismic velocity recovery. In general, the coseismic velocity changes increase with frequency. For the Iwate-Miyagi Nairiku earthquake, the strongest velocity changes occur close to the fault zone. Quickly recovering coseismic velocity changes can be separated from changes not recovering during the study period. For the Tohoku earthquake, the complete area is affected by coseismic velocity changes. A modelling of the depth of the coseismic velocity changes indicates that the Iwate-Miyagi Nairiku earthquake can be explained either by large shallow velocity changes or by small, but deep changes. For one station, the observations can only be explained by assuming deeper changes. For the Tohoku earthquake, the modelling shows that different parts of the study area are affected in different ways, some showing shallow changes, others deeper changes. Furthermore, seasonal velocity variations occur, which are compatible for the different stations above 0.5 Hz, with velocity maxima in autumn.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 90
    Publication Date: 2014-06-21
    Description: We report in this paper an original analysis of microseismic events (MSEs) induced by an excavation operation in the clay environment of the Mont Terri underground rock laboratory. In order to identify the MSEs with confidence, we develop a restrictive but efficient multistep method for filtering the recorded events. We deduce the spatial distribution and processes associated with the excavation-induced damage from the spatial location and focal mechanisms of the MSEs. We observe an asymmetric geometry of the excavation damaged zone around the excavated gallery, without notable microseismic activity in the sandy facies sidewall, in contrast with the shaly facies sidewall where a first burst of events is recorded, followed by two smaller bursts: one locates ahead of the excavation front and is associated with a dominant double-couple component, suggesting bedding plane reworking, that is, shear fracture mode, and the MSEs of the other cluster inside the shaly sidewall of the gallery, with a dominant compensated linear vector dipole component, suggesting extensive cracking. We identify and discuss four major factors that seem to control the MSEs source mechanisms: lithology, geometry of the geological features, gallery orientation and direction of the main compressive stress.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 91
    Publication Date: 2014-06-21
    Description: High-rate GNSS has attracted increasing attention and numerous applications in geohazard monitoring and early warning. In this paper, we investigate three current existing single-receiver approaches for real-time GNSS seismology, comparing their observation models for equivalence and assessing the impact of main error components. We propose some refinements to the variometric approach and especially consider compensating the geometry error component by using the accurate initial coordinates before the earthquake to eliminate the drift trend in the integrated coseismic displacements. After careful corrections of satellite ephemeris, ionospheric delay, tropospheric delay and geometry errors, the refined variometric approach and the temporal point positioning (TPP) method have equivalent mathematical model with the converged precise point positioning (PPP). We evaluated the precision of the variometric and TPP approaches with various error correction schemes and duration time using numerous data sets and demonstrated that few centimetres accuracy of coseismic displacements is achievable even for 20 min interval. We applied these single-receiver approaches to process 1 Hz GPS data collected from the Tohoku-Oki earthquake ( M w 9.0, 2011 March 11) in Japan to capture coseismic displacement, and further, inverted the obtained displacement fields for fault slip distribution and moment magnitude. Comparisons of the results obtained using the refined variometric approach and TPP, as well as the converged PPP, displayed very good consistence both in coseismic displacements within few centimetres and in the slip distribution patterns and moment magnitudes.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 92
    Publication Date: 2014-06-21
    Description: Macroseismic intensities are the only available data for most historical earthquakes and often represent the unique source of information for crucial events in the definition of seismic hazard. In this paper, we attempt at getting insight into source characteristics by reproducing the observed intensity field. As a test case, we study the source of 1908 Messina Straits earthquake ( M W  = 7.1), by testing three distinct fault models deduced from the analysis of geodetic data. Starting from the static slip distribution, we develop kinematic source models for the investigated fault and compute full waveform synthetic seismograms in a 1-D structural model, also accounting for anelastic attenuation. Then, we convert both computed peak-ground acceleration (PGA) and peak-ground velocity (PGV) to macroseismic intensity at 100 selected sites, by means of specific empirical relations for the Italian region. By comparing the original data separately with PGA- and PGV-based intensity fields, we discriminate among the tested faults and determine the best values for the investigated kinematic parameters of the source. We also perform a misfit analysis for the best source model, in order to investigate the dependence of the results on the selected parametrization. The results of the analysis indicate that among the tested models, the one characterized by an east-dipping fault, with strike-oriented NS slightly rotated clockwise, better explains the observed macroseismic field of the 1908 Messina Straits earthquake. Besides, the fracture nucleated at the southern end of the fault and ruptured northward, producing considerable directivity effects. This is in agreement with the published results obtained from the investigation of the historical seismograms. We also determine realistic values for the rupture velocity and the rise-time. Our study confirms the great potential of the macroseismic data, demonstrating that they contain enough information to constrain important characteristics of the fault, which can be retrieved by using complex source models and computing complete wavefield. Moreover, we also show that the simultaneous comparison of both PGA- and PGV-based synthetic macroseismic fields with the original intensities provides tighter constraints for discriminating among different source models, with respect to what attainable from each of them.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 93
    Publication Date: 2014-06-21
    Description: Perfectly matched layer (PML) is an efficient absorbing technique for numerical wave simulations. Since it appeared, various improvements have been made. The complex frequency-shifted PML (CFS-PML) improves the absorbing performance for near-grazing incident waves and evanescent waves. The auxiliary differential equation (ADE) formulation of the PML provides a convenient unsplit-field PML implementation that can be directly used with high order time marching schemes. The multi-axial PML (MPML) stabilizes the PML on anisotropic media. However, these improvements were generally developed for Cartesian grids. In this paper, we extend the ADE CFS-PML to general curvilinear (non-orthogonal) grids for elastic wave modelling. Unlike the common implementations to absorb the waves in the computational space, we apply the damping along the perpendicular direction of the PML layer in the local Cartesian coordinates. Further, we relate the perpendicular and parallel components of the gradient operator in the local Cartesian coordinates to the derivatives in the curvilinear coordinates, to avoid mapping the wavefield to the local Cartesian coordinates. It is thus easy to be incorporated with numerical schemes on curvilinear grids. We derive the PML equations for the interior region and for the free surface separately because the free surface boundary condition modifies the elastic wave equations. We show that the elastic wave modelling on curvilinear grids exhibits anisotropic effects in the computational space, which may lead to unstable simulations. To stabilize the simulation, we adapt the MPML strategy to also absorb the wavefield along the two parallel directions of the PML. We illustrate the stability of this ADE CFS-MPML for finite-difference elastic wave simulations on curvilinear grids by two numerical experiments.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 94
    Publication Date: 2014-06-21
    Description: Seismic monitoring can greatly benefit from imaging events with a low signal-to-noise ratio (SNR) as the number of the events with a low signal grows exponentially. One way to detect weaker events is improvement of a SNR by migration-type stacking of waveforms from multiple stations. We have developed a new method of location of seismic events that involves stacking of seismic phases and amplitudes along diffraction traveltime curves to suppress noise and detect seismic events with a SNR lower than that on individual receivers. The stacking includes polarity correction based on a simultaneous seismic moment tensor inversion and detection algorithm on the stack function. We applied this method to locate microseismicity induced by hydraulic fracturing. First we calibrated the velocity model by locating perforation shots at known locations. Then we processed 3 d of data from microseismic monitoring of shale stimulation and benchmarked migration-type locations of the largest events that were manually located. The detected and located events induced by hydraulic fracturing in this case study are mostly shear events forming narrow bands along the maximum horizontal stress direction approximately 100 m above the injection intervals. The proposed technique is fully automated and feasible for real-time seismic monitoring.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 95
    Publication Date: 2014-06-21
    Description: A series of six seismic events that occurred in one panel of Rudna copper-ore mine in Poland is studied. Although the events had comparable magnitudes, from 3.0 to 3.7, their ground effects were very diverse. Comparing the accelerations observed at various locations with their estimates from ground motion prediction equation the events split into three distinct pairs. The first pair ground effects exceed considerably the estimates at most of observation points, the second pair effects are abnormally high at short epicentral distances, whereas the third pair effects are much less than the estimates at most of observation points. The similarities in ground effects correlate with the fault mechanisms similarities. The first two pairs’ events, whose ground effects were strong, exhibit thrust faulting and the third pair events, which caused unexpectedly low ground motion exhibit normal faulting mechanisms. The paired events have also similar apparent stress values. These stress values of the two events of very weak ground effects are distinctly lower than the values of other four events. All events demonstrate dominating non-double-couple components in the overall mechanisms. A kinematic source analysis indicates that these events have extended rather than point sources, and five of them have distinct directivity effects. A static stress transfer analysis signifies interrelations between these events. The rupture of all events started in areas of Coulomb failure function increase due to the cumulative effect of previous events. Linking results of the ground effects, source, rupture and interaction analyses tentative geodynamic conclusions are formulated. The untypical and diverse ground effects of the studied events result likely from the events’ complexity expressed by tensile source mechanisms, finite sources, directivity of ruptures and nearly horizontal rupture planes. The above features seem to be implied by a superposition of coseismic alterations of stress field and stress changes due to mining. One cannot, therefore, exclude the possibility of other cases of significant deviations from the expected ground motion amplitudes, due to specific geodynamics in another parts of the mine. An analysis like that done within this work can allow, however, foreseeing such extreme surface impacts.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 96
    facet.materialart.
    Unknown
    Oxford University Press
    Publication Date: 2014-06-21
    Description: We present an epidemic type aftershock sequenc (ETAS) model where the offspring rates vary both spatially and temporally. This is achieved by distinguishing between those space–time volumes where the interpoint space and time distances are small, and those where they are considerably larger. We also question the nature of the background component in the ETAS model. Is it simply a temporal boundary correction ( t  = 0) or does it represent an additional tectonic process not described by the aftershock component? The form of these stochastic models should not be considered to be fixed. As we accumulate larger and better earthquake catalogues, GPS data, strain rates, etc., we have the ability to ask more complex questions about the nature of the process. By fitting modified models consistent with such questions, we should gain a better insight into the earthquake process. Hence, we consider a sequence of incrementally modified ETAS type models rather than ‘the’ ETAS model.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 97
    Publication Date: 2014-06-21
    Description: The calculation of first-order P -wave ray synthetic seismograms based on first-order ray tracing (FORT) and dynamic ray tracing (FODRT) for P -waves propagating in inhomogeneous, weakly anisotropic media is extended from smooth to layered media. All the basic formulae necessary to calculate the P -wave FORT and FODRT quantities inside layers and to transform them at the points of reflection/transmission are given. The proposed formulae are applicable in subcritical as well as overcritical regions. The accuracy of the results is tested by comparing the approximate (FORT) results with the results obtained from a standard ray tracer for anisotropic media. The tests indicate that, except for critical regions, where the ray theory provides incorrect results anyway, the accuracy of FORT and FODRT in layered media is comparable with the accuracy in smooth media.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 98
    Publication Date: 2014-06-21
    Description: We constrain azimuthal anisotropy in the West Antarctic upper mantle using shear wave splitting parameters obtained from teleseismic SKS, SKKS and PKS phases recorded at 37 broad-band seismometres deployed by the POLENET/ANET project. We use an eigenvalue technique to linearize the rotated and shifted shear wave horizontal particle motions and determine the fast direction and delay time for each arrival. High-quality measurements are stacked to determine the best fitting splitting parameters for each station. Overall, fast anisotropic directions are oriented at large angles to the direction of Antarctic absolute plate motion in both hotspot and no-net-rotation frameworks, showing that the anisotropy does not result from shear due to plate motion over the mantle. Further, the West Antarctic directions are substantially different from those of East Antarctica, indicating that anisotropy across the continent reflects multiple mantle regimes. We suggest that the observed anisotropy along the central Transantarctic Mountains (TAM) and adjacent West Antarctic Rift System (WARS), one of the largest zones of extended continental crust on Earth, results from asthenospheric mantle strain associated with the final pulse of western WARS extension in the late Miocene. Strong and consistent anisotropy throughout the WARS indicate fast axes subparallel to the inferred extension direction, a result unlike reports from the East African rift system and rifts within the Basin and Range, which show much greater variation. We contend that ductile shearing rather than magmatic intrusion may have been the controlling mechanism for accumulation and retention of such coherent, widespread anisotropic fabric. Splitting beneath the Marie Byrd Land Dome (MBL) is weaker than that observed elsewhere within the WARS, but shows a consistent fast direction, possibly representative of anisotropy that has been ‘frozen-in’ to remnant thicker lithosphere. Fast directions observed inland from the Amundsen Sea appear to be radial to the dome and may indicate radial horizontal mantle flow associated with an MBL plume head and low upper mantle velocities in this region, or alternatively to lithospheric features associated with the complex Cenozoic tectonics at the far-eastern end of the WARS.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 99
    Publication Date: 2014-06-21
    Description: We investigated the infrasound signals from seismic ground motions induced by North Korea's underground nuclear explosions, including the recent third explosion on 2013 February 12. For the third explosion, the epicentral infrasound signals were detected not only by three infrasound network stations (KSGAR, ULDAR and YAGAR) in South Korea but also by two nearby International Monitoring System infrasound stations, IS45 and IS30. The detectability of the signals was limited at stations located on the relatively east side of the epicentre, with large azimuth deviations due to very favourable atmospheric conditions for eastward propagation at stratospheric height in 2013. The stratospheric wind direction was the reverse of that when the second explosion was conducted in 2009 May. The source location of the epicentral infrasound with wave parameters determined at the multiple stations has an offset by about 16.6 km from the reference seismic location. It was possible to determine the infrasonic location with moderate accuracy by the correction of the azimuth deviation due to the eastward winds in the stratosphere. In addition to the epicentral infrasonic signals, diffracted infrasound signals were observed from the second underground nuclear explosion in 2009. The exceptional detectability of the diffracted infrasound was a consequence of the temporal formation of a thin atmospheric inversion layer over the ocean surface when the event occurred.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 100
    Publication Date: 2014-06-21
    Description: Field and laboratory observations show that seismicity has non-trivial period-dependent response to periodic stress perturbations. In Nepal, seismicity shows significant variations in response to annual monsoon-induced stress variations but not to semidiurnal tidal stresses of the same magnitude. Such period dependence cannot be explained by the Coulomb failure model and spring-slider rate-and-state model (SRM). Here, we study seismicity response to periodic stress perturbations in a 2-D continuum model of a rate-and-state fault (that is, a finite rate-and-state fault). We find that the resulting seismicity indeed exhibits nearly periodic variations. Their amplitude is maximum at a certain period, T a , and decreases with smaller and larger periods to the SRM predictions, remaining much larger than the SRM predictions for a wide range of periods around T a . We attribute the higher sensitivity of finite faults to their finite nucleation zones which vary in space and have a different slip-velocity evolution than that of the SRM. At periods T 〉〉 T a and T 〈〈 T a , the seismicity-rate variations are in phase with the stress-rate and stress variations, respectively, consistent with the SRM, although a gradual phase shift appears as T increases towards T a . Based on the similarities with the SRM and our simulations, we propose a semi-analytical expression for T a . Plausible sets of model parameters make T a equal to 1 yr, potentially explaining Nepal observations and constraining the fault properties. Our finite-fault findings indicate that a , where a is a rate-and-state parameter and is the effective normal stress, can be severely underestimated based on the SRM.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...